Link a few of the classes to implemented features/bugs in python

This adds comments that associate the classes we have for threading
usage to upstream bugs in python where similar features are being
created (and potentially supported upstream).

When we are able to reduce the number of supported python versions
we can/should try to remove our implementations and move to the ones
that may showup in the python standard library instead.

Change-Id: I7b58380aeb57a58fa3b3c424c9f39de30f44f0e9

taskflow/types/latch.py

@@ -20,7 +20,12 @@ from taskflow.types import timing as tt
 
 
 class Latch(object):
-    """A class that ensures N-arrivals occur before unblocking."""
+    """A class that ensures N-arrivals occur before unblocking.
+
+    TODO(harlowja): replace with http://bugs.python.org/issue8777 when we no
+    longer have to support python 2.6 or 2.7 and we can only support 3.2 or
+    later.
+    """
 
     def __init__(self, count):
         count = int(count)

taskflow/utils/lock_utils.py

@@ -142,6 +142,9 @@ class ReaderWriterLock(_ReaderWriterLockBase):
     the write lock.
 
     In the future these restrictions may be relaxed.
+
+    This can be eventually removed if http://bugs.python.org/issue8800 ever
+    gets accepted into the python standard threading library...
     """
     WRITER = 'w'
     READER = 'r'