Log Message:
Update php-xdebug to 2.5.3.

Mon, Apr 18, 2017 - xdebug 2.5.3

= Fixed bugs:

- Fixed issue #1421: Xdebug crashes when it is loaded without pcntl being
  present

Mon, Apr 17, 2017 - xdebug 2.5.2

= Fixed bugs:

- Fixed issue #701: Functions as array indexes show ??? in trace
- Fixed issue #1403: Code coverage does not cover BIND_STATIC
- Fixed issue #1404: Execution time is calculated incorrectly
- Fixed issue #1413: Code coverage mishap with PHP 7.1.3
- Fixed issue #1414: Missing variable assignment in traces with OPcache
  loaded
- Fixed issue #1415: Crash with multiple catch constructs with OPcache loaded
- Fixed issue #1416: Trace files should not include the first result of a
  generator if it hasn't started yet
- Fixed issue #1417: Fetching properties of static class contexts fails due
  to incorrect fetch mode
- Fixed issue #1419: Summary not written when script ended with
  "pcntl_exec()"