New dependency for unit testing: Googlemock

[Maximilian Kossick]

Hi guys,

I've added two unit tests that use mocks generated with Google's
opensource mock library. I'd like to add that library as build/run
time dependency for the unit tests. Only users that build the unit
tests with KDE4_BUILD_TESTS = ON will need that library. Are there any
objections to adding that dependency?

Cheers,
Max