Refactor use of math and other headers across the codebase.

* Delete mathstuff.h and defs.h.
* Move typedefs into util/types.h.
* Move definitions into util/defs.h.
* Use std::min and std::max for math_min and math_max.
* Replace math_clamp with a template function to prevent repeated sub-expressions.
* Add a Result enum for SoundSource::open() and SoundSource::parseHeader().
* Misc. other header-related cleanups.
Reword comment.
Fix narrowing-conversion issues by using std::fabs instead of fabs.
Fix more narrowing conversion errors.
Fix another math_min ambiguity.
Fix std=c++0x issue where 'using std::isnan;' collides with the new global-namespace version in c++11.
Add <iostream> in main.cpp.
Fix some ambiguities with use of pow().
Remove bitwise-fabs test since we don't use this anymore.
Move "#pragma intrinsic(fabs)" calls to util/math.h.
Fix EngineMasterTest by enabling master processing.
Add util/math.h to dlgprefreplaygain.h
Replace cmath.h with util/math.h in stat.cpp.
fix windows build