This allows us to compile the engine tests against the internal VAPI, so
we can unit test internal classes.
* CMakeLists.txt: Add top-level targets test-engine-run and
test-client-run that execute the respective test binaries. Make
the tests target depend on them and make them depend on their
binaries.
* Makefile.in: Add test-client and test-engin targets for convenience.
* src/CMakeLists.txt: Make the right invocation of valac to generate a
correct geary-engine-internal.vapi. Make gsettings schema generation
depend on geary-client so it exists for test-client if the main binary
hasn't been built.
* test/CMakeLists.txt: Split everything up into to builds, one for
test-engine and the other for test-client. Use geary-engine-internal
when building test-engine for access to internal classes and members.
* test/engine/util-idle-manager-test.vala,
test/engine/util-timeout-manager-test.vala: Use Glib MainContext rather
than the GTK main loop for pumping events so the test cases compile
without GTK.
* test/test-engine.vala, test/test-client.vala: New main source file for
test binaries based on old main.vala.
