Fixes #751 - Add staged_changes? check

[deepakmahakale]

Fixes #751

Add staged_changes? check to avoid stashing files if no changes have been staged.

stashing the files with no staged changes ends up deleting all files

[sds]

As you can see from the tests, this won't work.

In order to guarantee you are running checks against files that are staged or otherwise are the view that Git sees, we always need to stash any unstaged changes in tracked files.

The solution to this particular problem appears to be removing the --quiet flag from the call to git stash pop .... I'll do that in another PR.

[sds]

See 648383f.