test: Added a better PRNG (pseudorandom number generator)

test: Added a better PRNG (pseudorandom number generator)

This adds a fast SIMD-optimized variant of a small noncryptographic
PRNG originally developed by Bob Jenkins:
    http://www.burtleburtle.net/bob/rand/smallprng.html

The generated pseudorandom data is good enough to pass "Big Crush"
tests from TestU01 (http://en.wikipedia.org/wiki/TestU01).

SIMD code uses http://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html
which is a GCC specific extension. There is also a slower alternative
code path, which should work with any C compiler.

The performance of filling buffer with random data:
   Intel Core i7  @2.8GHz (SSE2)     : ~5.9 GB/s
   ARM Cortex-A15 @1.7GHz (NEON)     : ~2.2 GB/s
   IBM Cell PPU   @3.2GHz (Altivec)  : ~1.7 GB/s