Updated formula: libxml2

Adds a --with-python option, addressing Homebrew issue Homebrew/homebrew#2303:

  http://github.com/mxcl/homebrew/issues/issue/2303/

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

Fixes Homebrew/homebrew#2303
Fixes Homebrew/homebrew#3025

Formula/libxml2.rb

@@ -7,9 +7,23 @@ class Libxml2 <Formula
 
   keg_only :provided_by_osx
 
+  def options
+    # Works with the Python 2 formula
+    [['--with-python', 'Compile the libxml2 Python 2.x modules']]
+  end
+
   def install
     fails_with_llvm "Undefined symbols when linking", :build => "2326"
-    system "./configure", "--prefix=#{prefix}", "--disable-dependency-tracking"
+
+    args = ["--disable-dependency-tracking", "--prefix=#{prefix}"]
+
+    if ARGV.include? '--with-python'
+      python_prefix=`python-config --prefix`
+      ohai "Installing Python module to #{python_prefix}"
+      args << "--with-python=#{python_prefix}"
+    end
+
+    system "./configure", *args
     system "make"
     ENV.j1
     system "make install"