[perl #115928] a consistent (public) rand() implementation

Based on Yves' random branch work.

This version makes the new random number visible to external modules,
for example, List::Util's XS shuffle() implementation.

I've also added a 64-bit implementation when HAS_QUAD is true, this
should be significantly faster, even on 32-bit CPUs.  This is intended to
produce excactly the same sequence as the original implementation.
revert config_h.SH changes, now handled by Configure
[perl #115928] Configure now selects our internal drand48()