Get rid of clang warnings in plAvatar.
Fix more clang warnings.
Fix a clang warning.
Fix some compiler errors.
Remove unneeded wstring code in pfLocalizationMgr.
Correct plAvatar fixes.
Fix some plString/plFileSystem issues for *nix.
Standardize on C++ headers.

Also removes a bunch of duplicate #includes of stuff that's already
pulled in by HeadSpin.h.
math.h -> cmath
float.h -> cfloat
time.h -> ctime