drush features diff all

When I am done working on a branch, many times I have touched multiple features within the UI(we rely on features heavily) and want to see all the differences within drush.

Attached is a patch that does just that. The command "drush fda" will show all the features that are not in their default state then ask if you want to diff each one.

There is also exclude support: "drush fda feature_name1 feature_name2" will exclude feature_name1 and feature_name2 from the list of features to diff.

There is an option to force the diff without asking questions. This might come in handy if you know the diff will be small or if you want to force the output to go to a log file to review at another time. For example: "drush fda --force > ~/fda.log"