Merge branch '2.1' into 3.1

Conflicts:
	ChangeLog
Updated changelog
PHP 5.6 on travis does not yet have the changes PHP 5.5.10 has.

Assuming these changes will come in the future for the PHP 5.6 branch,
we're marking PHP 5.6 as an allowed failure until it's there.
Bumped version.
Merge branch '2.1' into 3.1

Conflicts:
	ChangeLog
	lib/Sabre/VObject/Version.php
Bumped version.
Merge branch '3.1'

Conflicts:
	ChangeLog
	lib/Sabre/VObject/Version.php