Update Gant to Homebrew Java style

Homebrew's preferred method for installing packaged software is to
install into the Cellar's libexec, and then symlink or wrap just
the binaries into bin.

Library/Formula/gant.rb

@@ -11,6 +11,10 @@ class Gant <Formula
  def install
  rm_f Dir["bin/*.bat"]
  # gant-starter.conf is found relative to bin
- prefix.install %w[bin lib conf]
+ libexec.install %w[bin lib conf]
+ (bin+'gant').write <<-EOS.undent
+ #!/bin/bash
+ exec #{libexec}/bin/gant
+ EOS
  end
 end