Well this is incredibly frustrating. After being nagged by Rails that I need to install the C-based MySQL adaptor, I did so... and then discovered that it won't work with MySQL under version 6. Now 'gem uninstall mysql' results in 'unknown gem mysql'.
I just spent half an hour trying to get the thing to install in the first place (by juggling all the "where the hell is my config file, anyway?" type of options).
Anyway, I can't find hints anywhere on how to use the ORIGINAL MySQL adaptor now that I've discovered that it's either that or an upgrade to MySQL 6, which I don't want to do since I'm using an XAMPP package that works very nicely already
(This is on my local box for testing, this is not a dev or production server issue. I'll deal with that later.)
So how do I either make sure Rails uses the built in version (using command line options?) OR remove the MySQL gem?
(Optional third option: Suck it up and upgrade my local copy of MySQL.)
edit: Turns out I was wrong about the version of MySQL I needed in the first place, and I fixed and upgraded a bunch of stuff.
However, my answer to the ORIGINAL question still stands: Delete the gem. If gem itself can't delete it, just delete all traces of it and RoR will default to the original adapter. This probably doesn't work in newer version of Rails, which (I think) REQUIRE the new adapter.