Create src-greenplum.r

Sorry for the separate pull request.  I'm having to enter the code via the website due to company firewalls.  I made the src-greenplum.r changes suggested.  Regarding has_lahman() are you suggesting edits to the data-lahman.r file?  I'm not sure I follow otherwise.  Unfortunately I don't have write access to the greenplum db so I'll be unable to really test some of the lahman stuff.