Doc generator fixes:

- enable contrib
- show __init__
- remove core.protobuf module
- fix bug in _get_arg_spec
- hide contrib.learn.head
Change: 146265365

Author: martinwicke

generate.py

@@ -118,8 +118,7 @@ def extract():
 
   # Access something in contrib so tf.contrib is properly loaded (it's hidden
   # behind lazy loading)
-  # TODO(wicke): Enable contrib traversal once contrib is sealed.
-  # _ = tf.contrib.__name__
+  _ = tf.contrib.__name__
 
   # Exclude some libaries in contrib from the documentation altogether.
   # TODO(wicke): Shrink this list.
@@ -163,6 +162,7 @@ def extract():
       ],
       'contrib.learn': [
           'datasets',
+          'head',
           'graph_actions',
           'io',
           'models',

parser.py

@@ -264,8 +264,8 @@ def _get_arg_spec(func):
       argspec_defaults = list(argspec.defaults[partial_args-first_default_arg:])
 
     first_default_arg = max(0, first_default_arg - partial_args)
-    for kwarg in func.keywords:
-      if kwarg in argspec.args:
+    for kwarg in (func.keywords or []):
+      if kwarg in (argspec.args or []):
         i = argspec_args.index(kwarg)
         argspec_args.pop(i)
         if i >= first_default_arg: