swift234

clean up the top level parser loop a bit: there are two scenarios here
that were (incorrectly) folded on top of each other: 1) multiple file mode,
and 2) parser pumping mode.  These modes were incompatible with each other
(and don't make sense together) so have the compiler reject attempts to make
use of them, and detangle the two cases from each other so that the flow is
more clear.



Swift SVN r5904