Re: Include extension path on pg_available_extensions

Hi Michael,

I am just getting started in the Postgres community (this is my first code review). So please excuse me if I have missed something (in terms of process etc).
I reviewed your proposed code changes in the attached patch file and they look good to me. I have some minor comments:

1. In src/test/modules/test_extensions/t/001_extension_control_path.pl, it would be nice if you could add a test that validates that the correct Extension location is displayed, if for example, the extension is being picked up from a customized location. 
2. Nit-pick: In src/backend/commands/extension.c:get_available_versions_for_extension(), you could probably combine the following 2 lines into one to say "'comment' & 'location' stay the same.
                    /* comment stays the same */                                                          
                   /* location stays the same */                                                                                                                                                                  

Hope this is helpful.

Thanks,
-Rohit