Hints for SiteTree.TreeTitle casting

Relates to SS-2013-009
Clearer escaping in ReportAdmin

No direct security issue since report titles can't be set by the user
FIX Escaping in "dependent pages" (SS-2013-009)
Clearer escaping in CMSMain

No direct security issue, but makes intent clearer
Merge pull request #853 from chillu/pulls/escape-3.1.0

Escaping 3.1