We spel gud.
Remove the eol.php special case for 5.3.29.

Instead, let's have an optional "eol" flag for releases in the $RELEASES array,
and use that to drive eol.php.
Use the new eol flag for an active release JSON feed.

This is mostly useful so the bug tracker can still get a list of active
releases when the QA site is down (cough, cough).
It would be nice to have the actual version number, too.