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: NMatt Kraai <matt.kraai@amo.abbott.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>