[bug] Add bug about GError
add bug 844/529
add bug 844/371
add bug 844/f7c
add 844/30b
bugs: File various new bugs
gvariant: Improve wording of excess varargs error message

Make it clearer that the error can be fixed by either removing the extra
vararg, or by adding a format string for it.
gvariant: Add a unit test for abusing g_variant_lookup()

This is the first real bug found in the wild by Tartan, in tp-glib.