Added a new method to deal with the build up of old tokens.

[mcondave]

Before adding the "oauth1_access_..." token, revoke any existing tokens for the user/consumer pair so the user's profile isn't flooded with old access tokens that are no longer applicable.

Related to the following issues:

#134
#131

[kosso]

I tried this. And while it did clear out all the old access_tokens, I could not log in to my app, despite it leaving one behind.

[mcondave]

@kosso Was an error message returned either on the client side or in your logs?

[kosso]

I've just tried this change again on 2.0-Beta15 and it appears to be working as expected now.

No more duplicate Application entries on the profile page from the same client.

Though, whether this is a desirable effect, I haven't quite decided.

eg: One 'universal' iOS client app installed on two devices (eg: an iPhone and an iPad).
Each time you logged in on one device, any stored token on the other device would be invalidated.