Update php-xdebug-devel to 2.6.0beta1

Changes:

Added features:

Fixed bug #1059: Add filter capabilities to tracing, stack traces, and code coverage.
Fixed bug #1437: Add X-Profile-File-Name header when a profile file has been generated.

Improvements:

Fixed bug #1493: Run test suite in AppVeyor for Windows CI.
Fixed bug #1498: Use new ZEND_EXTENSION API in config.w32 build scripts. (Kalle)

Fixed bugs:

Fixed bug #702: Check whether variables tracing also works with =&.
Fixed bug #1501: Xdebug var dump tries casting properties.
Fixed bug #1502: SEND_REF lines are not marked as covered.

(jdolecek)