[CM] GC Called recursively

[bil at ccrma.Stanford.EDU]

> Are there rules about what can and can't be done in a 'mark' function?

Sorry about the empty message -- the cancel button is right
next to the send button in raoundcube -- pessimal UI.

On the original question -- don't allocate anything in s7 in
the mark function -- that could trigger a recursive call,
I think, though I've never tried it.

I'm a great believer in print statements.  If you need
to drop into gsb without calling abort, there's a dummy
function gdb_break -- handy for arbitrary break points.