Fix an invalid memcpy identified by valgrind.

* subversion/libsvn_subr/sorts.c
  (svn_priority_queue__pop): Use memmove as memory blocks overlap, tweak
   whitespace.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1572175 13f79535-47bb-0310-9956-ffa450edef68