Up warning level to -Wall/extra/error for non-MSVC
Up warning level to -Wall/extra/error for non-MSVC

UTPP_AMPLIFY_WARNINGS can be turned OFF to disable the new behavior.

grahamreeds/unittest-cpp,pjohnmeyer/unittest-cpp,pjohnmeyer/unittest-cpp,unittest-cpp/unittest-cpp,unittest-cpp/unittest-cpp,grahamreeds/unittest-cpp,grahamreeds/unittest-cpp,unittest-cpp/unittest-cpp