lib: move IsSimilarMagnitude and downcasters here from single modules
where they're used
acpi: simplify by only using v1.0 or 2.0 tables
snd: add note on why OpenAL can't be used
mahaf: change prefix
wcpu: cache results, reinstate wcpu_ClockFrequency
win: add winreg.h for registry functions
wsnd: only do the DSound thing on non-vista (and delay-load to avoid
overhead)
wutil: add code to correctly detect windows version
This was SVN commit r5090.
