Allow building with xmlparse.h

expat 1.1 and 1.2 provide xmlparse.h instead of expat.h.  Include the
former on systems that define the EXPAT_NEEDS_XMLPARSE_H variable and
define that variable on QNX systems, which ship with expat 1.1.

Signed-off-by: Matt Kraai <matt.kraai@amo.abbott.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'jk/read-commit-buffer-data-after-free' into pu

Will merge to 'next'.

* jk/read-commit-buffer-data-after-free:
  log: re-encode commit messages before grepping
Merge branch 'mk/old-expat' into pu

* mk/old-expat:
  Allow building with xmlparse.h