fix readline extension compilation against readline 6.3

readline 6.3 removed some typedefs that had been deprecated for some time, but
Python 2.7.6 still uses them and therefore fails to build the readline
extension when it is enabled. This issue has been addressed in the Python bug
tracker here: http://bugs.python.org/issue20374. The patch below is based on
the readline_func_cast.patch patch uploaded there. Also see
http://lists.gnu.org/archive/html/bug-readline/2014-03/msg00003.html for more
information.

This patch should be removed with the next Python 2.7 release, which should
include the fix.

Signed-off-by: Ivan Sergeev <vsergeev@kumunetworks.com>

diff -purN python-2.7.6.orig/Modules/readline.c python-2.7.6/Modules/readline.c
--- python-2.7.6.orig/Modules/readline.c	2014-04-16 13:40:17.566874715 -0700
+++ python-2.7.6/Modules/readline.c	2014-04-16 13:37:15.421231983 -0700
@@ -911,12 +911,12 @@ setup_readline(void)
     rl_bind_key_in_map ('\t', rl_complete, emacs_meta_keymap);
     rl_bind_key_in_map ('\033', rl_complete, emacs_meta_keymap);
     /* Set our hook functions */
-    rl_startup_hook = (Function *)on_startup_hook;
+    rl_startup_hook = on_startup_hook;
 #ifdef HAVE_RL_PRE_INPUT_HOOK
-    rl_pre_input_hook = (Function *)on_pre_input_hook;
+    rl_pre_input_hook = on_pre_input_hook;
 #endif
     /* Set our completion function */
-    rl_attempted_completion_function = (CPPFunction *)flex_complete;
+    rl_attempted_completion_function = flex_complete;
     /* Set Python word break characters */
     completer_word_break_characters =
         rl_completer_word_break_characters =