RUN-PROGRAM fails to clean-up the handler that it added with
ADD-FD-HANDLER if it exits due to error rather then EOF.
So when user does RUN-PROGRAM with a stream that encounters any
encoding errors or such, any subsequent RUN-PROGRAM's are hosed
because of a stale FD handler left in the *descriptor-handlers*
Attached patch fixes it, and adds a test case. This fixes the bug that
user dsp_ was describing on #lisp with pdfinfo output on a barf.pdf