Fix the following error:
```
# >>>> make_forks()
Cloning into '/tmp/galaxy_release_test_cQZHDb9B/work'...
done.
+ cd /tmp/galaxy_release_test_cQZHDb9B/work
+ git config user.name 'Test User'
+ git config user.email test@example.org
# Checking out ref '9bddbada0d3f7835ecafd12220a76dcfb6e3daca' as 'dev'
+ git checkout --no-track -b dev 9bddbada0d
fatal: A branch named 'dev' already exists.
```
Also:
- Add `log_exec` to a few git commands
- Convert release Makefile targets to a script
- Update package versions from Galaxy version instead of leaving them
uncoupled
- Use next-dev-version process on release branches when in between point
releases
- Automatically detect and increment versions
- Test merging release branches forward before pushing releases
- Support multiple rc versions (will be more useful for package testing)
- Support building local versions of packages
- Tests for the release script
Dannon Baker