Add formula for plt-racket (formerly plt-scheme)

Signed-off-by: David Höppner <0xffea@gmail.com>

* remove white spaces
* use new macro snow_leopard_64?
* ruby chdir

Formula/plt-racket.rb

@@ -0,0 +1,29 @@
+require 'formula'
+
+class PltRacket <Formula
+  # There are source packages but the OSX package is a .dmg and the Unix
+  # tarball doesn't have everything needed for building on OSX
+  url 'git://github.com/plt/racket.git', :tag => 'v5.0.1'
+  homepage 'http://racket-lang.org/'
+  version '5.0.1'
+
+  # executables work fine until clean step calls strip on them
+  skip_clean 'bin'
+
+  def install
+    Dir.chdir 'src' do
+
+      args = [ "--disable-debug", "--disable-dependency-tracking",
+              "--enable-xonx",
+              "--prefix=#{prefix}" ]
+
+      if snow_leopard_64?
+        args += ["--enable-mac64", "--enable-sgc", "--disable-gracket"]
+      end
+
+      system "./configure", *args
+      system "make"
+      system "make install"
+    end
+  end
+end