Integrate SFMT 1.3.3 into test infrastructure.

Integrate the SIMD-oriented Fast Mersenne Twister (SFMT) 1.3.3 into the
test infrastructure.

The sfmt_t state encapsulation modification comes from Crux
(http://www.canonware.com/Crux/) and enables multiple
concurrent PRNGs.

test/unit/SFMT.c is an adaptation of SFMT's test.c that performs all the
same validation, both for 32- and 64-bit generation.