Ability to trace mocks

[thoni56]

Sometimes it is hard to figure out which calls to mocks did fail. Especially if you have a long sequence of calls to functions like getChar() or similar, a trace would be handy.

cgreen_mocks_are(tracing_mocks);

would be a very handy way to activate trace printouts on stdout like:

Mock <function> called with <args> returning <value>