dub: Use Alternate Dependency

[jmh530]

I'm working on two related dub projects on code.dlang.org. One 
has a dependency on the other. However, I've made changes to both 
and to run the tests properly requires me to use both versions in 
my working directory, rather than the versions (specifically for 
the dependency) that is registered on dub.

How do I ensure that dub picks up the right version?