Improve failure to run script errors.
Improve failure to run script errors.

Add a special case (and clear message) for directory, avoid spewing a
pointless backtrace, and always report on stderr.

cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp,cygx/nqp