calc 2.15.1.2 release

The following are the changes in this release:

Removed use of HAVE_MEMMOVE as well have_memmv.c.  Removed the
building and including of have_memmv.h.  Removed the memmove()
function in blkcpy.c, used when HAVE_MEMMOVE was NOT defined.
The libc memmove(3) function as defined by <string.h> is now
required to compile calc because the replacement code in
blkcpy.c q was problematic, especially when regions overlap.
The HAVE_MEMMOVE make symbol was removed from Makefile.config.
Thanks to GitHub user @skeeto for reporting this problem.