Following up on r1599552, tweak code for compatibility with git.

* subversion/libsvn_client/diff.c
  (diff_content_changed): Add missing headers.

* subversion/libsvn_diff/binary_diff.c
  (write_literal): Properly read unsigned characters.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1599595 13f79535-47bb-0310-9956-ffa450edef68