Code review comment for lp:~jameinel/bzr/quick-fix

Fixes some issues with fetch + ghosts + smart server
Turns out that my update for gc stacking slightly regressed our ability to push 'bzr.dev' via the smart server, because of how missing inventories and ghosts interact.

This patch adds tests that assert we can fetch via smart server for *all* formats with a revision that has a ghost parent (a test which was missing w/ Andrew's fix). It also adds similar tests for fetching revisions w/ ghosts into a stacked branch. (Which Andrew's original fix did *not* address.)

Both StreamSource and GroupCHKStreamSource were affected by this, though there are still more failures with --dev6 + stacking + smart server code to be fixed. (Namely 'bzr push bzr+ssh://.../new-branch' fails because the smart remote client tries to 'upgrade' the default branch to a hard-coded 1.6.1/1.6-rich-root format repository)