Extension: dep <library> switch <branch-name>

[currycoder]

dep <library> switch <branch-name>

Currently, when you want to switch a working copy's dependency libraries to a particular branch, you have to do this sort of thing:

dep gn-django checkout develop
dep gn-django pull
dep gn-django checkout <branch>

The proposal here is to shortcut this with dep <library> switch <branch-name> which does all of the above.

There could be an extended shortcut; dep switch <branch-name> which attempts this for all dependencies (assuming common branch naming for a particular feature set). If the branch is not present for a particular dependency, it is left on develop.