LDM libdir/libexecdir merge request, other fixes

Please merge https://code.launchpad.net/~bcgss/ltsp/+git/ldm-rhel7 to ldm upstream.

List of changes, grouped:

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gcc warning fixes and whitespace removal:

commit b6ad7db3d2a8c5d7aadff111b8e5ef5c3710c477
Author: Kim B. Heino <email address hidden>
Date: Fri Jun 16 16:32:13 2017 +0300

    ssh: fix logging error and two gcc warnings

commit a0612211faa5069008d49d722409e20493395959
Author: Kim B. Heino <email address hidden>
Date: Fri Jun 16 16:31:38 2017 +0300

    ssh: remove trailing whitespaces

commit 8da40c8a2dd516e0f43e82f57b797094c61ed12c
Author: Kim B. Heino <email address hidden>
Date: Fri Jun 16 16:30:25 2017 +0300

    greeter: fix gcc warning

commit c2baad2e15f9130e3fdacf1bf4055299dc724dcb
Author: Kim B. Heino <email address hidden>
Date: Fri Jun 16 16:30:00 2017 +0300

    ldmutils: fix gcc warning

commit 57949728e8ff064301ec5dc4e2116f0f53a1947e
Author: Kim B. Heino <email address hidden>
Date: Fri Jun 16 16:51:35 2017 +0300

    ldm: g_type_init is deprecated in new glib

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Flush log file, simple fix:

commit 26bdf33864472ab31e8ff0c578588ae5b738cede
Author: Kim B. Heino <email address hidden>
Date: Fri Jun 16 16:27:29 2017 +0300

    logging: flush log file after each write

    Debugging ldm crash was quite hard when log file was missing last lines.
    Logging is quite minimal so flushing it after each line does no harm.

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nc will hang forever waiting for eof if stdin is not devnull or similar file. Make sure it is. This is needed in rhel7. Maybe change to socat instead of nc in future?

commit cabcd37a9354e59c257dd55196c215a32c89f40b
Author: Kim B. Heino <email address hidden>
Date: Fri Jun 16 16:38:05 2017 +0300

    screen.d/ldm: make sure nc's input is null, hide "Connection refused" error

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This is bigger/important fix. In src/plugins/ Makefile you use libdir for *.so (as you should), but in top level src/ Makefile you use libexecdir for same *.so files. Result is that ldm searches plugins from wrong directory. Fix top level Makefile to use libdir for plugins.

I think at least Debian has libdir == libexecdir, so this has no change there. In rhel7 this is important fix as libdir != libexecdir.

commit 4485221eb6714ddae79ac99cd5d93030e8e71d26
Author: Kim B. Heino <email address hidden>
Date: Fri Jun 16 16:33:33 2017 +0300

    Makefile: use same ldmplugdir value as in src/plugins/

    In RHEL7 plugins are installed to /usr/lib64/ldm (libdir/ldm) and
    executables to /usr/libexec/ldm (libexecdir/ldm).