handle PHP < 5.4 with ENT_XML1 native constant that doesn't exists

git-svn-id: https://plugins.svn.wordpress.org/events-manager-ess/trunk@814260 b8457f37-d9ea-0310-8a92-e5e31aec5664
handle PHP < 5.4 with ENT_XML1 native constant that doesn't exists
prevent PHP E_STRICT and E_WARNINGS to be displayed on user screen.

git-svn-id: https://plugins.svn.wordpress.org/events-manager-ess/trunk@814261 b8457f37-d9ea-0310-8a92-e5e31aec5664