Reduce compiler warnings on gcc, clang, icc, and MinGW

These changes severely reduce compiler warnings. Some changes are really bug fixes, such as the %z format specifier not being recognized by MinGW in OSD_MAllocHook.cxx (otherwise z's would be printed in place of those values) and some required parentheses in TDataStd_NamedData.cxx for the proper results.

As stated in the mailing list, I mainly targeted the warnings that accounted for the majority of the volume of warnings, and lone warnings which only popped up once, which are probably unintended mistakes.