Performance over network mounts

[smashwilson]

I work on files over a mount, and running merge-conflicts takes about 3-4 minutes to load.

Is it possible to ask it to only search a particular folder in the tree rather than everything in the current tree?

This is tricky because we're using git to do most of our file I/O, but we should test and consider ways we can make the git experience better on slow filesystems.

/cc smashwilson/merge-conflicts#270 @redmoss