* cygtls.h (_cygtls::inside_kernel): Move function declaration into _cygtls

* cygtls.h (_cygtls::inside_kernel): Move function declaration into _cygtls
class.
* exceptions.cc (_cygtls::inside_kernel): Move function definition into _cygtls
class.
* fhandler.cc (fhandler_base::wait_overlapped): Make return tri-state to detect
when there is a EINTR situation.  Add a pointer to a length parameter.  Move
GetOverlappedResult into this function.
(fhandler_base::read_overlapped): Accommodate above changes and loop if we
receive a restartable signal.
(fhandler_base::write_overlapped): Ditto.
* fhandler.h (fhandler_base::wait_overlapped): Reflect above changes.
* fhandler_fifo.cc (fhandler_fifo::wait): Ditto.