Added support for C++11 strongly typed enums

C++11 enum classes were previously not compatible with CHECK_EQUAL and CHECK_ARRAY_EQUAL due to not being implicitly convertable to an int.

eg enum class Colour : short { Red, Blue };

To use uncomment
#define UNITTEST_FORCE_CPP11_DETECTION in Config.h

Test cases for strongly typed enums can be enabled by invoking cmake with -DUTPP_USE_CPP11 option
What about clang, others?