According to [this](http://docs.python.org/2/library/warnings.html), DeprecationWarning is ignored by default.  But we could easily just write a deprecation message.  I think it would also be useful to have it print the command that it is actually running. e.g.
```
$ galsim_yaml demo1.yaml
Note: galsim_yaml has been deprecated.  Use galsim instead.
Running galsim -f yaml demo1.yaml
...
```