Added LibXDiff

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Formula/libxdiff.rb

@@ -0,0 +1,15 @@
+require 'formula'
+
+class Libxdiff <Formula
+  url 'http://www.xmailserver.org/libxdiff-0.23.tar.gz'
+  homepage 'http://www.xmailserver.org/xdiff-lib.html'
+  md5 '8970281543130411d8a1b1f004a8418b'
+
+  def install
+    system "./configure", "--disable-debug",
+                          "--disable-dependency-tracking",
+                          "--prefix=#{prefix}",
+                          "--mandir=#{man}"
+    system "make install"
+  end
+end