PHP 5.3 compat.
Merge branch '1.7' into 1.8
CalendarQueryValidator works with vobject 2.1 and 3.0.

Travis now tests with both versions of the library.
Merge branch '1.7' into 1.8

Conflicts:
	lib/Sabre/CalDAV/CalendarQueryValidator.php
Merge branch '1.8'

Conflicts:
	.travis.yml
	lib/Sabre/CalDAV/CalendarQueryValidator.php