Improve HTTP status handling. Allow 203 as an alternative to 200 OK.

Improve HTTP status handling. Allow 203 as an alternative to 200 OK.
Most other 2xx status codes are still not expected and therefor considered
an error. The GET requests issued by this code should not result in other
2xx result codes.
Also handle and ignore the 1xx Informational headers but again only 100
and 103 are handled and 101 Switching Protocols and 102 Processing are
not expected and are considered an error.
OK deraadt@