Update test Makefile to find dSFMT 2.2.

Tests now compile out of the box following 80c59523.
Update comments and make dsfmt_get_min_array_size public.
Procedures for getting a small arrays of random numbers.

The minimum dsfmt array size is actually quite large (O(10^2)) and
getting small numbers of random numbers one-at-a-time from the internal
store comes with an overhead which can easily be avoided.