Added 'sources' to the Git ignores.
Merge pull request #314 from jalcine/feature/ignoring-thy-sources

Ignoring Your Sources
Export PS4 when RBENV_DEBUG is set for more informative debug output
Add `rbenv --debug <command>` as a shortcut for setting RBENV_DEBUG=1
Suppress shell warnings when hashing is disabled by `set +h`
Guard against exported `CDPATH` (fixes #316)