test-driver: Use a single driver which supports both tap and simple

Rename our GTest tap compiler so it's clearer what's going on.
Makefile.am: Add check-memory target for valgrind testing

Update the test-driver to accomodate this and figure out
how best to implement this.

Fix up 'make recheck' as well.
glib.supp: Add valgrind suppression of uninitiaziled sigaction
libsecret: Fix uninitialized access in _secret_attributes_validate()
Makefile.am: Fix make distcheck again
Makefile.am: Don't build tests during normal builds

This makes things build faster, and also fixes issues
I can't reproduce with vala and gir.

https://bugzilla.gnome.org/show_bug.cgi?id=725690
tap-gtester: Set a standard environment variable for test harness

Lets tests know whether they're running under an automated
testing harness.
Release version 0.18