* fhandler.h (fhandler_base::has_ongoing_io): Declare virtual method.

* select.cc (peek_pipe): Reorganize slightly.  Don't attempt to check a handle
if it has ongoing I/O.
(select_pipe_info::select_pipe_info): Delete definition.
(select_pipe_info::~select_pipe_info): Delete definition.
(thread_pipe): Get rid of WFMO call.  Reorganize loop.
(pipe_cleanup): Remove dependence on destructor.
(thread_serial): Reorganize loop.
* select.h (select_pipe_info): Empty this class since it no longer has any
special requirements (for now).
* syscalls.cc (readv): Remove an unneeded debug printf.

winsup/cygwin/fhandler.h

@@ -386,6 +386,7 @@ class fhandler_base
   bool issymlink () {return pc.issymlink ();}
   bool device_access_denied (int) __attribute__ ((regparm (2)));
   int fhaccess (int flags, bool) __attribute__ ((regparm (3)));
+  virtual bool has_ongoing_io () {return false;}
 };
 
 class fhandler_mailslot : public fhandler_base