Speed up insertion of subprocess output on MS-Windows.

Speed up insertion of subprocess output on MS-Windows.

 src/ralloc.c (resize_bloc, r_alloc_sbrk): Don't call memmove if its
 first 2 arguments are identical.  This makes inserting large
 output from a subprocess an order of magnitude faster on
 MS-Windows, where all sbrk'ed memory is always contiguous.