No more vicious error circle on tq errors
I've eliminated the annoying *spurious* popup produced by tq, so that
Geiser can recover from error conditions arising from unexpected
input to a transaction queue that has no active transaction. We now
log the offending input and keep going.
Greg, over at racket's list, reported such a happening when leaving
the REPL after C-u C-c C-z; but i've been unable to reproduce the
problem. Probably, we have a bug lurking somewhere that this patch
doesn't fix, but at least it should work as a palliative.