Did you edit the .htaccess file?
No, it's currently disabled. But I'll need to enable again for furls.
Mostly harmless.
Try deleting all the files in the core/cache directory and clearing your browser cache and cookies. You may be getting a cached version of index.php from before you reverted it.
D'oh, of course, the old "delete cache files" trick. Thank you!
Mostly harmless.
I'm glad it worked for you.
Was planning to upgrade from 2.1.3 to 2.1.5 if nothing else worked...
Mostly harmless.