Provide both safe (default) and fast variants of math_clamp()
Use specialized CSAMPLE_clamp() where appropriate
Use math_clamp_fast() where min/max parameters are constants
math_clamp_safe() should always print a warning upon invalid bounds
Use SampleUtil for clamping sample values
Rename math_clamp_fast() to math_clamp_unsafe()
Improve math_clamp_safe() by not changing the value on invalid bounds

..and reorder parameters in the warning message to reflect their order
in the function definition.
Replace obsolete comment
Unit tests for math_clamp_safe/unsafe()
Merge pull request #390 from uklotzde/math_clamp_variants

New math_clamp() variants