Delete the python xdg dependency.

BUG=RH#980749

Review URL: https://codereview.appspot.com/10930043
Load the system registry cache prior to the user one.

gnome-settings-daemon runs ibus-daemon after the user configures
any input method engines and causes a delay to show the engines
on UI because no cache exists for ibus-daemon.
The system cache can avoid the user timing.

Review URL: https://codereview.appspot.com/10364043
Delete xdg in ibus-setup.

Review URL: https://codereview.appspot.com/11100044
build: fix make check

This contains several fixes to the current tests:

- Remove glib mem profiler call from src/tests, which is known not to
  work with the latest glib release:
  https://bugzilla.gnome.org/show_bug.cgi?id=701694
  valgrind could be used instead.

- Replace g_type_init() call in tests with ibus_init().

- Fix ibus-bus test after the DBus property change (commit 458945e7).
  no global engine may be set in the test environment.  Also add more
  assertions to check the return values.

- Fix pygobject test to use LOG_COMPILER and move sys.path adjustment
  into the test script itself.

- Add new files to po/POTFILES.in.

BUG=
R=takao.fujiwara1@gmail.com

Review URL: https://codereview.appspot.com/11156043
registry: use binary format instead of XML for cache

Currently the registry cache is in the XML format, that may cause
unnecessary parsing overhead on ibus-daemon startup.  This patch
changes the format to GVariant based binary representation.

BUG=
R=takao.fujiwara1@gmail.com

Review URL: https://codereview.appspot.com/9963043