TestHost can't check that SourceScripts is unmodified anymore because
C4ScriptHost contains a std::unique_ptr these days, so we can't copy
derived classes. Next best thing is just creating two instances of
TestHost and comparing those.
GTest does not ship precompiled binaries anymore. They are now compiled
using the CMakelists.txt from gtest.
Add basic unit tests for C4Value, DirectExec and C4StringTable.
Nicolas Hake