The server and the client both looked for "upgrade" as a substring of the
Connection field value, so "notupgrade", "upgrade-not" and "xupgrade" all
passed as the standalone token the handshake requires. RFC 6455 4.2.1 asks
for an ASCII case-insensitive token match, and a value split across several
Connection lines was missed entirely because only the first line was read.
Parse the field as the comma-separated token list it is, across every line,
and reuse the same helper for the server request check and the client
response check.
Reported by gb1dev.
dc02475152
