Add back some deprecated and general purpose API tests. These are the
ones that were written already pretty much conforming to the GTest API
and style, and thus require minimal porting.
It's the conformance test suite: there's no need to namespace the files,
just like there's no need to namespace the units.
This commit does not change the Cogl tests: they will be moved to Cogl
over time, and it's easier to do if we leave them as they are.
