Match SIP_Version case-insensitively.

RFC 3261 Section 7.1:
  The SIP-Version string is case-insensitive,
  but implementations MUST send upper-case.
Normalize message_header name case.

RFC 3261 Section 7.3.1:
  When comparing header fields, field names are always case-insensitive.
Fix display_name rule.

1. Reverse sub-expression order.
2. Don't include quotes in the value of a quoted_string.