Log Message:
add patches from upstream to fix possible crashes and memory corruption
on malformed input (CVE-2016-0718)
Description: The Expat XML parser mishandles certain kinds of malformed
input documents, resulting in buffer overflows during processing and error
reporting. The overflows can manifest as a segmentation fault or as memory
corruption during a parse operation. The bugs allow for a denial of service
attack in many applications by an unauthenticated attacker, and could
conceivably result in remote code execution.

bump PKGREV

also add an improvement to the fix for CVE-2015-1283 which was part
of the 2.1.1 release -- don't rely on defined behaviour on overflows
of signed integer operations, from upstream git:
https://sourceforge.net/p/expat/code_git/ci/f0bec73b018caa07d3e75ec8dd967f3785d71bde/

pkgsrc change: add a hint how to run the pkg's selftest (not enabled
permanently because this would add a dependency on C++)