The report generation was broken by the split of the various test units;
also, we were using GTest in a way that's not really sanctioned by
upstream.
This commit tries to re-use the targets from GLib's Makefile rules while
compensating for our own set up.
I was fed up to cd into the tests/conform or tests/interactive directories
to launch a specific test. Now, with the power the abs_ variants of
builddir and srcdir we can run specific test from any directory.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2159
