Renamed compiler detecting test app.
Added CCompilerDetectingTestApp and use this to check that the c compiler is being used.
Changed TestApp so that it models the library and executable as separate TestComponents.
Removed some more convention mappings.
Removed Clang on cygwin as a supported tool chain (for now).
Mentioned some more nice features in the native languages support.
Added some more detail about what stuff from cygwin is required.
Added a few more open issues to the native languages spec.