Allowing arguments to be passed to _python

I'm brand new to fish so I'm not sure if this is a fix of if I'm doing something incorrectly.  On fish version 2.1.0 on osx 10.9.2 running pyhttp doesn't start the http server, instead only starts the python shell.  This fixes that issue for me at least.

plugins/python/_python.fish

 # Use python2 if found, otherwise fallback to python.
 function _python
   if which python2
-    python2
+    python2 $argv
   else
-    python
+    python $argv
   end
 end