Fix thinko in hash keys test
Move tests to their proper place

Moves tests for #ref and #unref to their logical place under
TestFundamentalObject, even though we need TestFundamentalSubObject to
actually test them. This eliminates two skips.
Fix indenting
Support :object types as vfunc return values
Add tests for remaining refcount testing vfuncs
Add skip guards
Support vfuncs returning :object types [merges 'vfunc-returning-object']
Add test for gvalue_flat_array_round_trip

The given skip reason is no longer true, so no implementation changes
are needed.
Add test for test_interface_test_int8_in

A mechanism to implement interfaces now exists, so this function can be
tested. The test passes.
Unify skip descriptions for unimplemented methods
Add a TODO item
Explain skips with references to open GNOME bugs
Clarify skip description