Fix session creation without encryption (no aes) (#156)

In the absence of AES support by the cryptographic module, an exception
was thrown at session creation time.

Author: gberaudo

Diff for: beaker/session.py

@@ -567,7 +567,7 @@ def __init__(self, request, key='beaker.session.id', timeout=None,
 
         self.crypto_module = get_crypto_module(crypto_type)
 
-        if not self.crypto_module.has_aes and encrypt_key:
+        if encrypt_key and not self.crypto_module.has_aes:
             raise InvalidCryptoBackendError("No AES library is installed, can't generate "
                                             "encrypted cookie-only Session.")