RFC 7230: server MUST reject messages with BWS after field-name (#445)

RFC 7230: server MUST reject messages with BWS after field-name (#445)

Obey the RFC requirement to reject HTTP requests with whitespace
between field-name and the colon delimiter. Rejection is
critical in the presence of broken HTTP agents that mishandle
malformed messages.

Also obey requirement to always strip such whitespace from HTTP
response messages. The relaxed parser is no longer necessary for
this response change.

For now non-HTTP protocols retain the old behaviour of removal
only when using the relaxed parser.