libusb: Add head

-HEAD includes several bug fixes
-This should also be "kinect-friendly" Homebrew/homebrew#5307

Closes Homebrew/homebrew#9646.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Formula/libusb.rb

@@ -4,6 +4,7 @@ class Libusb < Formula
   url 'http://downloads.sourceforge.net/project/libusb/libusb-1.0/libusb-1.0.8/libusb-1.0.8.tar.bz2'
   homepage 'http://www.libusb.org/'
   md5 '37d34e6eaa69a4b645a19ff4ca63ceef'
+  head 'git://git.libusb.org/libusb.git'
 
   def options
     [["--universal", "Build a universal binary."]]
@@ -11,6 +12,7 @@ class Libusb < Formula
 
   def install
     ENV.universal_binary if ARGV.build_universal?
+    system "./autogen.sh" if ARGV.build_head?
     system "./configure", "--prefix=#{prefix}", "--disable-dependency-tracking"
     system "make install"
   end