* fhandler.h (fhandler_virtual::exists): Eliminate path argument.

* fhandler.h (fhandler_virtual::exists): Eliminate path argument.
(fhandler_proc::exists): Ditto.
(fhandler_registry::exists): Ditto.
(fhandler_process::exists): Ditto.
* fhandler_proc.cc (fhandler_proc::exists): Ditto.  Use built-in name.
* fhandler_process.cc (fhandler_process::exists): Ditto.
(fstat): Ditto.
* fhandler_registry.cc (fhandler_registry::exists): Ditto.
(fhandler_registry::fstat): Ditto.
* fhandler_virtual.cc (fhandler_virtual::opendir): Ditto.
* path.cc (path_conv::check): Ditto.  Add debugging.
* syscalls.cc (dup): Always call dup2 for error handling.