Allow parallel building and testing by using a single Makefile.am
Implement parallel testing using TAP, with various drivers and
compilers living in the build/ directory.
Fix all sorts of issues that this caused, including builddir != srcdir,
leaks in tests and so on.
It would have been nice to break out all the above into separate
commits ... blush.
* Death by a thousand paper cuts from gir and vapi not liking
the fact that the secret.h file was not usable uninstalled
and installed in the same way.
