[metapost] results-caching bugs

[Doug McIlroy]

If this is the wrong forum for reporting bugs, please
point me in the right direction.  I didn't see how
to do it at the metapost project home page.

Bug 1.
mpost apparently "optimizes" its behavior by doing nothing
if it can find output lying around that seems to have
come from the given input.  This caused me no end of
confusion when I tried, on the same input, both mpost
and mpost -T.  Unless one knows enough to remove the
outputs between commands, one gets identical results from
both.  By definition they are supposed to be different.

Bug 2.
After a failure, mpost leaves useless output lying
around. This is bad form in general.  But it's
doubly bad when it exacerbates Bug 1.  (Perhaps
this has something to do with interactivity.  I
naively respond "q" to the error prompt.)

Doug McIlroy