Reviewers: mp+219608_code.launchpad.net,

Message:
Please take a look.

Description:
Extract errors package to github.com/juju/errors

Also introduces a dependency on github.com/juju/errgo
and removes the github.com/errgo/errgo dependency.

Adds additional functions for simple tracing and
annotations of errors.

https://code.launchpad.net/~thumper/juju-core/juju-errors/+merge/219608

(do not edit description out of merge proposal)


Please review this at https://codereview.appspot.com/93410043/

Affected files (+254, -658 lines):
   A [revision details]
   M agent/agent.go
   M agent/tools/toolsdir.go
   M cert/cert.go
   M cmd/juju/bootstrap_test.go
   M cmd/juju/common.go
   M cmd/juju/debuglog.go
   M cmd/juju/debuglog_test.go
   M cmd/juju/deploy_test.go
   M cmd/juju/destroyenvironment_test.go
   M cmd/juju/removemachine_test.go
   M cmd/jujud/agent.go
   M cmd/jujud/bootstrap_test.go
   M cmd/jujud/machine.go
   M cmd/jujud/machine_test.go
   M constraints/constraints.go
   M container/kvm/container.go
   M container/kvm/kvm.go
   M container/lxc/instance.go
   M dependencies.tsv
   M environs/bootstrap/state.go
   M environs/bootstrap/synctools.go
   M environs/cloudinit.go
   M environs/cloudinit/cloudinit.go
   M environs/config.go
   M environs/config/config.go
   M environs/configstore/disk.go
   M environs/configstore/disk_test.go
   M environs/configstore/mem.go
   M environs/emptystorage.go
   M environs/emptystorage_test.go
   M environs/filestorage/filestorage.go
   M environs/filestorage/filestorage_test.go
   M environs/httpstorage/storage.go
   M environs/httpstorage/storage_test.go
   M environs/imagemetadata/generate.go
   M environs/jujutest/livetests.go
   M environs/jujutest/tests.go
   M environs/open.go
   M environs/open_test.go
   M environs/simplestreams/datasource.go
   M environs/simplestreams/simplestreams.go
   M environs/sshstorage/storage.go
   M environs/sshstorage/storage_test.go
   M environs/tools/simplestreams.go
   M environs/tools/tools.go
   M environs/tools/tools_test.go
   D errors/errors.go
   D errors/errors_test.go
   M juju/api.go
   M juju/apiconn_test.go
   M juju/conn.go
   M juju/conn_test.go
   M provider/azure/certfile.go
   M provider/azure/environ.go
   M provider/azure/instance.go
   M provider/azure/instancetype.go
   M provider/azure/storage.go
   M provider/azure/storage_test.go
   M provider/common/destroy_test.go
   M provider/dummy/storage.go
   M provider/ec2/ec2.go
   M provider/ec2/storage.go
   M provider/joyent/environ_instance.go
   M provider/joyent/storage.go
   M provider/joyent/storage_test.go
   M provider/local/environ.go
   M provider/local/instance.go
   M provider/maas/environ.go
   M provider/maas/environ_whitebox_test.go
   M provider/maas/storage.go
   M provider/maas/storage_test.go
   M provider/manual/environ.go
   M provider/openstack/provider.go
   M provider/openstack/storage.go
   M state/addmachine.go
   M state/annotator.go
   M state/api/agent/machine_test.go
   M state/api/client.go
   M state/api/machiner/machiner_test.go
   M state/api/provisioner/provisioner_test.go
   M state/api/uniter/unit_test.go
   M state/api/upgrader/unitupgrader_test.go
   M state/api/upgrader/upgrader_test.go
   M state/apiserver/admin.go
   M state/apiserver/charmrevisionupdater/updater.go
   M state/apiserver/charmrevisionupdater/updater_test.go
   M state/apiserver/charms.go
   M state/apiserver/client/api_test.go
   M state/apiserver/client/client.go
   M state/apiserver/client/client_test.go
   M state/apiserver/client/destroy_test.go
   M state/apiserver/client/status.go
   M state/apiserver/common/errors.go
   M state/apiserver/common/errors_test.go
   M state/apiserver/common/password_test.go
   M state/apiserver/deployer/deployer_test.go
   M state/apiserver/firewaller/firewaller_test.go
   M state/apiserver/keymanager/keymanager.go
   M state/apiserver/keyupdater/authorisedkeys.go
   M state/apiserver/machine/machiner.go
   M state/apiserver/provisioner/provisioner_test.go
   M state/apiserver/uniter/uniter.go
   M state/apiserver/uniter/uniter_test.go
   M state/apiserver/upgrader/unitupgrader_test.go
   M state/apiserver/upgrader/upgrader_test.go
   M state/charm_test.go
   M state/cleanup.go
   M state/cleanup_test.go
   M state/configvalidator_test.go
   M state/conn_test.go
   M state/constraints.go
   M state/environ.go
   M state/environcapability_test.go
   M state/machine.go
   M state/machine_test.go
   M state/megawatcher.go
   M state/minimumunits.go
   M state/open.go
   M state/policy.go
   M state/prechecker_test.go
   M state/relation.go
   M state/relation_test.go
   M state/relationunit.go
   M state/relationunit_test.go
   M state/service.go
   M state/service_test.go
   M state/settings.go
   M state/settings_test.go
   M state/state.go
   M state/state_test.go
   M state/status.go
   M state/tools_test.go
   M state/unit.go
   M state/unit_test.go
   M state/user.go
   M state/watcher.go
   M worker/authenticationworker/worker.go
   M worker/deployer/deployer_test.go
   M worker/firewaller/firewaller.go
   M worker/instancepoller/aggregate.go
   M worker/instancepoller/aggregate_test.go
   M worker/instancepoller/machine_test.go
   M worker/instancepoller/updater.go
   M worker/peergrouper/mock_test.go
   M worker/peergrouper/worker.go
   M worker/provisioner/kvm-broker_test.go
   M worker/provisioner/lxc-broker_test.go
   M worker/provisioner/provisioner.go
   M worker/provisioner/provisioner_test.go
   M worker/rsyslog/worker.go
   M worker/uniter/charm/bundles.go
   M worker/uniter/relation/relation.go
   M worker/uniter/relationer_test.go
   M worker/uniter/state.go
   M worker/uniter/uniter_test.go
   M worker/upgrader/upgrader_test.go