Added proof for #439.
Fixed the implementation of PATCH so it makes sense again. #439.
Updated changelog
Merge branch '1.7' into 1.8

Conflicts:
	lib/Sabre/DAV/FSExt/File.php
	lib/Sabre/DAV/PartialUpdate/Plugin.php
More bugfixes for #439.
Merge branch '1.7' into 1.8

Conflicts:
	lib/Sabre/DAV/PartialUpdate/Plugin.php
Merge branch '1.8'

Conflicts:
	ChangeLog
	lib/Sabre/DAV/FSExt/File.php
	lib/Sabre/DAV/PartialUpdate/Plugin.php
	tests/Sabre/DAV/PartialUpdate/PluginTest.php
Merge branch 'master' of github.com:fruux/sabre-dav
Making the tests pass for master as well. #439