Fix phpdoc for DateTime variables and arguments
Work around hhvm not being able to modify a date with 'first day of this month'

see https://github.com/facebook/hhvm/issues/1469
workaround DateTime->modify() always advancing the date even if the current day is a  in hhvm
adjust test case to work around hhvm returning a binary string from utf8_encode
hhvm is not allowed to fail.
Merge remote-tracking branch 'icewind1991/hhvm-compat' into hhvm
Merge branch 'master' into hhvm

Conflicts:
	lib/Sabre/VObject/RecurrenceIterator.php
	tests/Sabre/VObject/StringUtilTest.php
Merge branch 'master' into hhvm
Merge branch 'master' into hhvm