JIT: remove unnecessary pxor in paired stores

I don't think this is necessary anymore?
Remove runtime OS X version check.

My recent update to that check broke compilation on 10.9:
https://code.google.com/p/dolphin-emu/issues/detail?id=7900

However, on further review, the check isn't actually necessary.  If the
OS X version is older than LSMinimumSystemVersion in Info.plist, the
system will generally refuse to run the binary in the first place.  You
can try to launch it via a terminal, but at that point it's the user's
problem if it crashes.
Merge pull request #1627 from comex/remove-version-check

Remove runtime OS X version check.
Merge pull request #1619 from FioraAeterna/removepxor

JIT: remove unnecessary pxor in paired stores
Think of this as rough draft. Taking suggestions to make it robust, error free, and prettier!

For more information:
https://docs.google.com/document/d/1tBEgsJh7QiwNwepXI0eobfK3U8LkJButSyeuFt1degM/edit?usp=sharing

removed: SSE includes

added: 16bit -> float -> 16bit functions
added: linear interpolator and high-quality interpolator functions (including Resampler class)
added: dithering

changed: renamed variables and reformatted a few things to fit with style guide
changed: use s16, u16, s32, u32 etc
changed: store samples and do all computations as floats
changed: volume from 0 - 255
Merge https://github.com/dolphin-emu/dolphin into FIR-interpolator