* fhandler.h (fhandler_base::pread): Declare new function.

* fhandler.h (fhandler_base::pread): Declare new function.
(fhandler_base::pwrite): Ditto.
(fhandler_disk_file::pread): Ditto.
(fhandler_disk_file::pwrite): Ditto.
* fhandler.cc (fhandler_base::pread): Define new function.
(fhandler_base::pwrite): Ditto.
* fhandler_disk_file.cc (fhandler_base::pread): Ditto.
(fhandler_base::pwrite): Ditto.
* syscalls.cc (pread): Define new function.
(pwrite): Ditto.
* cygwin.din: Export pread, pwrite.
* include/sys/ioctl.h: Guard some _IO* declarations to avoid conflict with
socket.h.