Populate HTTP warning codes

Includes changing 201 "Server Error" to "Internal Server Error"
List mostly borrowed from here http://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml
418 and 451 also added
Local testing showed a problem with 202 reported as "Server Error" instead of "Accepted"

stat - function result cache

Set the correct json content-type

Chance text/json to application/json to comply with the RFC.

See http://www.ietf.org/rfc/rfc4627.txt for more information.

Change printf mask %zu -> %lu

 for MS VC++ compatibility http://stackoverflow.com/questions/15610053/correct-printf-format-specifier-for-size-t-zu-or-iu

Disallow WebDAV MKCOL/PUT/DELETE requests to protected files