workaround for cffi issue 140. refs #762
make create_modulename private, add test
be less dumb
Don't go via hex() when working with BNs
Added backend check to hash primitives
Added backend check to hmac primitives
Added backend check to cipher primitives
Added backend check to rsa primitives
RSAPrivateKey to evp_pkey utility method
Just EVP_PKEY GC free the contained keys.

Fortunately we never use these bare.
Fixed style nitpick
Style nitpick
Style nitpick
Style nitpick
Merge pull request #804 from Ayrx/add-backend-check-to-hashes

Added backend check to hash primitives
Merge pull request #805 from Ayrx/add-backend-check-to-hmac

Added backend check to hmac primitives
Merge pull request #806 from Ayrx/add-backend-check-to-cipher

Added backend check to cipher primitives
Merge pull request #807 from Ayrx/add-backend-check-to-rsa

Added backend check to rsa primitives
Fix circular imports with available_backends()
Tiny style changes to some imports