Moved the IE content type checks to their own class. Disassembled IE 5 and 6 and...

Moved the IE content type checks to their own class. Disassembled IE 5 and 6 and added the results to the class. The entry points now return an array giving MIME types for all versions. The most important version difference is the introduction of an early check for PNG headers in IE 7. Added application/x-msdownload to disallowed types, haven't been able to reproduce any vulnerability, but it's better to be on the safe side.