Cothread: Create cosocket.create_connection function

Seems silly not be wrapping this basic helper function.

git-svn-id: svn+ssh://serv0002.cs.diamond.ac.uk/home/subversion/repos/controls/diamond/trunk/python/cothread@113114 e099a375-04f9-0310-9d5f-a741eaff62e1
Cothread: Export server_close() and use it in tests

To avoid warnings in tests it is necessary to actually close the
listening socket using the undocumented server_close() function.

Signed-off-by: Michael Davidsaver <mdavidsaver@bnl.gov>

git-svn-id: svn+ssh://serv0002.cs.diamond.ac.uk/home/subversion/repos/controls/diamond/trunk/python/cothread@113115 e099a375-04f9-0310-9d5f-a741eaff62e1