Add project dependency

The integration test is currently failing, and I've no idea how to it to work.

The point of failure is in the function `cljr--add-project-dependency` which actually writes to `project.clj`.  In order to open this file we call `cljr--project-file`.  This function is used in several other ecukes tests, where it performs admirably, but in this case it claims `project.clj` is a file in the `clj-refactor` dir instead of in `clj-refactor/tmp` dir.  The result is a failing regexp search when an empty file is opened instead of the project file.

I would _REALLY_ like to fix this problem, because I think it's important to exercise the entire feature and the integration between `nrepl-refactor` and `clj-refactor`, but I'd also like to merge this code in, at some point, because this feature is quite handy!

@rejeep can you think of any reason for this problem?  Anyone else have any ideas? @magnars @AlexBaranosky @benedekfazekas