add support for installing fltk 1.3

The stable 1.1.x series of fltk is very old and is no longer being maintained.
The 1.3.x series is expected to replace it as the new stable series soon. This
commit adds the ability to install the current snapshot of 1.3.x by using
--HEAD; this is needed by Octave 3.4's new plotting mode.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/fltk.rb

@@ -3,9 +3,19 @@ require 'formula'
 class Fltk < Formula
   url 'http://ftp2.easysw.com/pub/fltk/1.1.10/fltk-1.1.10-source.tar.gz'
   homepage 'http://www.fltk.org/'
-  md5 'e6378a76ca1ef073bcb092df1ef3ba55'
+  head 'http://ftp.easysw.com/pub/fltk/snapshots/fltk-1.3.x-r8411.tar.bz2'
+  if ARGV.build_head?
+    md5 '0c44ccd5d9b86c7afb2f402d5e0b56db'
+    depends_on 'jpeg'
+  else
+    md5 'e6378a76ca1ef073bcb092df1ef3ba55'
+  end
 
   def install
+    if ARGV.build_head?
+      ENV.libpng
+      system "autoconf"
+    end
     system "./configure", "--prefix=#{prefix}", "--enable-threads"
     system "make install"
   end