Added a test for extra CRLF lines in keep-alive connections
Support for non-RFC compliant header prefixes

When using keep-alive connections, some HTTP implementations insert unexpected and extra CRLF tokens between each connection, which can result in the next request being prefixed with a CRLF.

Some other client/server implementations are tollerant of this, and for example this bug doesn't show up when using the Go net/http library.