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
s/available_backends/_available_backends/
s/set1/assign/
Merge pull request #812 from public/circular-fix

Fix circular imports with available_backends()
Merge pull request #811 from alex/import-style

Tiny style changes to some imports