increase string length (from rails default of 255) to 2048 for redirect_uri columns to accommodate longer URIs; 2048 selected by consulting http://stackoverflow.com/questions/417142/what-is-the-maximum-length-of-a-url and picking a power of two
Do not try to load unavailable Request class for the current phase.

If you send grant_type=code for token request for example, you'll see
runtime exceptions such as:

  undefined method `pre_auth'; for #<Doorkeeper::TokensController:0x007fe04b7aa778>

Since grant_type comes as a request parameter, it's better to
explicitly limit the available request implementations rather than
trying to load the class and rescue constant lookup failures.
Always issue an access token upon request

Returning the existing token when there was one accessible let to
issues when dealing with multiple authorization methods.

Once the resource owner authorized the app on the web, while the token
was still fresh, the r.o. would authenticate using a mobile app -
using any flow - and the previous existing token would be revoked.

This would break the web app, since the token it was being used got
revoked.

Mentioned in issue #191
Add integration spec for multiple device sign-in #191
Releasing v0.7.1
Merge pull request #272 from miyagawa/multiple-sessions-0.7

Allow issuing multiple access_tokens for one user/application for multiple devices
Merge pull request #170 from panarom/master

increase length of redirect_uri columns
Updates dummy app migration and schema
Merge pull request #239 from miyagawa/explicit_strategies

Do not try to load unavailable Request class for the current phase.
Add owner fields to dummy app
relax jquery-rails gem dependency
Merge pull request #273 from miyagawa/relax-jquery

Relax jquery-rails gem dependency
Include missing routes generated in README
Merge pull request #274 from huoxito/readme-patch

Include missing routes generated in README
Fix small typo
Merge pull request #276 from kerrizor/patch-1

Fix small typo
Releasing v0.7.2