Litecoin: Runtime detection of SSE2 32bit x86 for Scrypt

* x86_64 and Intel MacOS X always uses scrypt-sse2, non-x86 uses scrypt-generic.
* x86 (not Mac) detects cpuid features and chooses sse2 or generic during runtime.

How to Build with SSE2 Support
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* make litecoind with USE_SSE2=1
* qmake with USE_SSE2=1
Litecoin: Upgrade gitian win32 to Precise 12.04 and boost-1.54

mingw upgrade allows more hardening, compiler bug fixes and possibily win64 later.
Rename deps .zip files to be more consistent in revision format.

Litecoin: Reuse bitcoin-0.9 win32 deps.
Litecoin: SSE2 scrypt unit test coverage