Add option to get rid of "unknown" in exception diagnostic message

[Pavel Machyniak <machyniak@…>]

I think it would be nice to have option to exclude from exception diagnostic string messages like "Throw in function (unknown)" and only include those if the context is known.

Reason: those messages usually do not add any information.

For example:

Throw in function (unknown)
Dynamic exception type: struct Exceptions::TestException
std::exception::what: Unknown exception
[struct Exceptions::ErrorCode_ *] = 123

Would become:

Dynamic exception type: struct Exceptions::TestException
[struct Exceptions::ErrorCode_ *] = 123

[Emil Dotchevski]

Trunk revision 70989