Merge pull request #439 from cstrouse/add-optipng

Add optipng (0.7.6) package

packages/optipng.rb

+require 'package'
+
+class Optipng < Package
+  version '0.7.6'
+  source_url 'http://prdownloads.sourceforge.net/optipng/optipng-0.7.6.tar.gz'
+  source_sha1 '3b3e31430e735589470c4af204354d38823f4989'
+
+  # NOTE: uses libpng and zlib but uses its own versions of those libraries
+
+  def self.build
+    system "./configure --prefix=/usr/local"
+    system "make"
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install" 
+  end
+end