Fix tests.

This includes fixes for running the tests on OSX.

For example, `sh -c "echo -n ..."` on OSX doesn't catch "-n" as an argument and puts it in the file. This changes the commit hashes that we are checking for. `bash -c "echo -n ..."` solves this problem, and is still compatible with *NIX (Ubuntu, etc.).

This PR requires beyang/hgo#1 to be pulled first, or the tests will still fail on the ResolveBranch test with the brew version of Mercurial (3.0.2).