Updated CDATA wrappers in script blocks when a non-xhtml doctype has been set.

CDATA wrappers in script blocks are only useful for CDATA in XHTML doctypes.  In non-XHTML doctypes, they are just noise.

With this change, if the HtmlHelper::docType method was called with a non-XHTML doctype, the CDATA wrapper will not be set by default (can still be turned on with the `safe` option set to true)