Allow metarefresh module to specify the permissions of the resulting files,...

Allow metarefresh module to specify the permissions of the resulting files, overriding the default 0600. Contributed by Dick Visser.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@3260 44740490-163a-0410-bde0-09ae8108e29a