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"
Merge pull request #407 from kuiash/master

Populate HTTP warning codes