gcc 4.9.1 inc patch

Mimics the official Homebrew’s version bump from 4.8.3 to 4.9.1, kills
off the -HEAD option, removes the now defunct patch for gcc on DP3 in
favour of James Clarke’s new DP4 patch. Also accepts James Clarke’s
proposed OS X Tiger tidying up - Whether this remains is largely
conditional on the official Homebrew accepting it imminently.