Make warnings fatal and add options to control warnings.

Warnings mess up the coverage recording process and scripts
generally shouldn't have them. If this is a problem for testing
existing scripts, they can be disabled by passing
CMAKE_UNIT_NO_DEV_WARNINGS=TRUE or
CMAKE_UNIT_NO_UNIITIALIZED_WARNINGS=TRUE
Updates to build scripts.

1. Warn about unused variables
2. Submit windows test coverage to coveralls
3. Cache CMake installer download on Windows
4. Test with both VS and NMake on Windows
Fix problems with tracing on Windows - cut line at first ):, not :

This prevents catching the drive letter as the end of the line
Reduce IO by buffering reads and writes more efficiently
Merge pull request #43 from smspillaz/cmake-unit.item_41

Fix tracing problems on Windows