* include/bits/random.h (mersenne_twister_engine): Don't inline
discard here. New member function _M_gen_rand.
* include/bits/random.tcc (mersenne_twister_engine<>::_M_gen_rand):
New function. Extracted from operator().
(mersenne_twister_engine<>::discard): New implementation which
skips in large steps.
(mersenne_twister_engine<>::operator()): Use _M_gen_rand.
From-SVN: r190711