Use current stable as maximum allowed GLib version

GLib 2.32 is the current version on Ubuntu 12.04 LTS, therefore the
GLIB_VERSION_2_36 macro is not defined and the sanity check in
/usr/include/glib-2.0/glib/gversionmacros.h fails.
Merge pull request #6 from matze/fix-ubuntu-build

Use current stable as maximum allowed GLib version