OSX version still needs a bit of work, but completely works now (#43)

setup/py2app.patch

@@ -0,0 +1,12 @@
+--- original-util.py	2014-06-17 12:50:15.000000000 -0700
++++ util.py	2014-06-17 12:51:33.000000000 -0700
+@@ -148,6 +148,9 @@
+     log.info("copying file %s -> %s", source, destination)
+     with zipio.open(source, 'rb') as fp_in:
+         if not dry_run:
++            if os.path.exists(destination):
++                os.unlink(destination)
++
+             with open(destination, 'wb') as fp_out:
+                 data = fp_in.read()
+                 fp_out.write(data)