Fix an issue with tr on OS X

The version of tr that ships with OS X can't handle certain binary
inputs if the locale is set to a certain value. This sets the locale
to C.
Merge pull request #18 from lorin/osx-fix

Fix an issue with tr on OS X
Exit when directory doesn't contain a .git dir

- this prevents the following error, when initializing in a non-git directory

/usr/local/bin/gitcrypt: line 96: .git/info/attributes: No such file or directory
/usr/local/bin/gitcrypt: line 97: .git/info/attributes: No such file or directory
/usr/local/bin/gitcrypt: line 98: .git/info/attributes: No such file or directory
error: could not lock config file .git/config: No such file or directory
error: could not lock config file .git/config: No such file or directory
error: could not lock config file .git/config: No such file or directory
error: could not lock config file .git/config: No such file or directory
error: could not lock config file .git/config: No such file or directory
error: could not lock config file .git/config: No such file or directory
Merge pull request #25 from kechagia/git-check

Exit when directory doesn't contain a .git dir
bump version for release
Release version 0.3.1