Skip rsa tests when dependencies not met

[jayvdb]

Fixes issue #164

[singingwolfboy]

Rather than doing this four-line check, I'd suggest doing this at the top of the file:

try:
    import cryptography
except ImportError:
    cryptography = None

and then using the skipUnless() decorator on tests that require the cryptography module:

@unittest.skipUnless(cryptography, "cryptography module is required")
def test_signature_methods(self, generate_nonce, generate_timestamp):
    # ...

[jayvdb]

I've moved the import at the top.
Unfortunately skipUnless isn't available on Python 2.6's unittest, and using monkey patching for that is going too far IMO. We could switch to using unittest2 on Python 2.6.

[jayvdb]

Travis build with revised patch and the #168 patch: https://travis-ci.org/jayvdb/requests-oauthlib/builds/82236300

[Lukasa]

Why are we bothering to print anything here?

[jayvdb]

So that the unittest output shows something useful. i.e.
https://travis-ci.org/jayvdb/requests-oauthlib/jobs/82236301#L176

[jayvdb]

Do you want me to add unittest2 support so that this workaround is needed?

[Lukasa]

That might be better, yeah.