Change the way we confirm success for creating temp repos

This change allows Windows machines to pass hesokuri.git-test. Before this
change, we looked for the .git directory in the output of git init to confirm
everything worked. However, msysgit outputs the path in a different form than
what is normal (/ instead of \, e.g. "C:/Users/JDoe/foo"). So now, just use
throw-if-error to confirm success.

Note that searching for "Initialized empty Git repository", though tempting,
does not work for localized environments.
Configure user information for temporary repos during testing

This is needed to avoid errors when doing 'git commit' during unit tests, since
this needs to read user.name and user.email config values. Git reports an error
if they are set neither globally nor on the repo.
Merge pull request #15 from matvore/windows-compat-error

Fix logic for creating temporary repos in tests