* devices.in (dev_storage): Map /dev/zero and /dev/full to \Device\Null.

* devices.cc: Regenerate.
	* dtable.h (struct dtable): Make fhandler_base friend, rather
	than fhandler_disk_file.
	* fhandler.cc (fhandler_base::open_with_arch): Create unique id.
	(fhandler_base::cleanup): Call del_my_locks.
	(fhandler_base::fcntl): Handle F_GETLK, F_SETLK and F_SETLKW.
	* fhandler.h (fhandler_base::get_dev): Return real device number.
	(fhandler_base::set_unique_id): New inline method.
	(fhandler_disk_file::lock): Drop declaration.
	(fhandler_disk_file::get_dev): New method, return pc.fs_serial_number.
	(fhandler_dev_zero::open): Drop declaration.
	* fhandler_disk_file.cc (fhandler_disk_file::close): Move
	del_my_locks call to fhandler_base::open_with_arch.
	(fhandler_disk_file::fcntl): Move handling of locking commands to
	fhandler_base::fcntl.
	(fhandler_base::open_fs): Drop call to NtAllocateLocallyUniqueId.
	* fhandler_zero.cc (fhandler_dev_zero::open): Remove so that default
	fhandler_base::open is used to open \Device\Null.
	* flock.cc (fixup_lockf_after_exec): Finding a single fhandler is
	enough here.
	(fhandler_base::lock): Replace fhandler_disk_file::lock.  Refuse to lock
	nohandle devices.  Handle read/write test using POSIX flags.  Explain
	why.  Never fail on SEEK_CUR or SEEK_END, rather assume position 0,
	just as Linux.
	* net.cc (fdsock): Create unique id.

winsup/cygwin/dtable.h

@@ -90,7 +90,7 @@ public:
   friend void dtable_init ();
   friend void __stdcall close_all_files (bool);
   friend int dup_finish (int, int, int);
-  friend class fhandler_disk_file;
+  friend class fhandler_base;
   friend class cygheap_fdmanip;
   friend class cygheap_fdget;
   friend class cygheap_fdnew;