Pythonize and add some more comments.
Small refactoring of handle_read().

Let's not have two call sites of sendMessageWrapper() when we can have
one.
Split add_socket() to two functions.
Some more refactoring and docs on the add_socket() area.
Split imports to multiple lines.

http://www.python.org/dev/peps/pep-0008/#imports
Remove unused pyasn1_modules import.