autogenerate files with constants

To add constants to pyzmq:

1. make appropriate changes to utils/constant_names.py
2. run buildutils/updateconstants.py
run update constants
remove explicit constants from CFFI backend
use libzmq-3 API for creating / destroying contexts in CFFI backend
test constant logic
update constant_names after testing
re-run updateconstants
test new and removed containers against reality
update integer sockopt test

with new name for FAIL_UNROUTABLE
move constant templates into their own files

which are textually included in the 'real' files

rather than making the files themselves templates.
add `setup.py constants`
typos in constant_names
Merge pull request #399 from minrk/constants

autogenerate files that involve constants

To add constants to pyzmq:

1. make appropriate changes to utils/constant_names.py
2. run `python setup.py contants`

No longer need to edit half a dozen files all over the place when a new constant is added, it should be just the one.