Document all of the BGL algorithms that are available in the Python bindings.

In some cases, tweak the implementations where they didn't make sense.


[SVN r28344]

libs/graph

@@ -1 +1 @@
-Subproject commit 9fe51b2a58539461be8bef90e5383e4c316d526a
+Subproject commit efc05efebd028201d4bd8c1e0bf237dd087de925