Be compatible with Ubuntu 12.04 'precise'-based systems
shim: Add a minimal fallback version of PKG_CHECK_VAR
We can't just drop in an updated version of pkg.m4, because older versions of pkg.m4 didn't have a serial number, so an older system copy would overwrite our local copy.
( :'-( )
Skip GLib tests when GLib is older than 2.38
GLib 2.38 was the first stable release with TAP output support, and our unit test relies on that.