Enable us to have regression testing by introducing a core testing
framework that uses the GLib JUnit-like test library.
Do this by adding a new subdir app/tests that will contain all our
tests (it contains one trivial test already). Also add app/tests.[ch]
with a new function gimp_init_for_testing() so that test cases can
easily setup the core object system.
Enable silent build rules by default, requires at least
Automake-1.11. Disable by either passing --disable-silent-rules to
configure or passing V=1 to make.