Integrate the Google C++ Mocking Framework

I thought it would be better to have not just _gtest_, but _gmock_ available, even if only for its "matchers" library.

I see that you worked through a bunch of concessions earlier in file _src/wrap/gtest-wrapper.h_. I'm not sure if we'll need similar concessions for the _gmock_ files. I'm building so far on Linux, and don't see warnings coming out of _make_ for now.