Errors in _pkcs11.pyx file: change operand "is" by "=="

[aglao83]

Hello,

There are errors in file _pkcs11.pyx that lead to a wrong behavior of the module.

In class:
cdef class MechanismWithParam under the tag "# Unpack mechanism parameters".

Please change the following:
1)
if mechanism is Mechanism.RSA_PKCS_OAEP
by
if mechanism == Mechanism.RSA_PKCS_OAEP

elif mechanism is Mechanism.AES_ECB_ENCRYPT_DATA
by
elif mechanism == Mechanism.AES_ECB_ENCRYPT_DATA

elif mechanism is Mechanism.AES_CBC_ENCRYPT_DATA
by
elif mechanism == Mechanism.AES_CBC_ENCRYPT_DATA

The "is" operand should not be used to compare enumerate and leads to wrong behavior if enumerates with large int values (>256) are compared. The best practice is to use the "==" operand instead when comparing enumerates.
This part of the code does not work as intended as the compared int values are large:
AES_ECB_ENCRYPT_DATA = 4356
AES_CBC_ENCRYPT_DATA = 4357

You can test the "is" operand problem with int value > 256 as follow:

a=5
b=5
a is b
True

a=300
b=300
a is b
False

Thanks