support --backend as a pytest flag to limit to one backend for testing
pass posargs via tox so --backend can be used for tox envs
don't mutate _ALL_BACKENDS
better name for the variable
modify backend selection to allow multiple backends via comma delimiter
docs for explicit backend selection and document name attribute of backend
revert fixture decorator for now, switch to append. no more globals
update docs for name attribute
fix docs
add cipher support to the commoncrypto backend
update changelog for commoncrypto backend
add error handler
add comment and change gc for cipher context
change cipher registry to store enums
expand tox backend example
make register_cipher_adapter private and fix cryptorref release
Remove register_cipher_adapter from the interface and the documentation.
Merge pull request #468 from reaperhulk/backend-flag-pytest

Add backend flag for pytest runs
experiment to disable duplicate cc test runs on osx and speed up travis
move some dashes around :)