* fhandler_netdrive.cc (struct netdriveinf): New structure to
store thread arguments.
(thread_netdrive): Thread handling all potentially blocking
WNet... calls.
(create_thread_and_wait): Start and wait for above thread.
(fhandler_netdrive::exists): Change to call create_thread_and_wait
instead of calling WNet... function.
(fhandler_netdrive::readdir): Ditto. Fix error handling.
(fhandler_netdrive::rewinddir): New method.
return code from GetFileSize and set file size to 0 if necessary.
* fhandler_netdrive.cc (fhandler_netdrive::fstat): Set permissions
to read/execute for all.
* dir.cc (mkdir): Check path for writability.
(rmdir): Ditto. Remove check for special directories.
* path.cc (path_conv::check): Set PATH_RO for virtual devices. Set error if
read-only and asked for writability.
* path.h (pathconv_arg): Add PC_WRITABLE.
(path_types): Add PATH_RO.
(path_conv::isro): Add (currently unused) check for read-only filesystem.
Return "ENOSHARE" when we know a share doesn't exist.
* include/sys/mount.h: Add MOUNT_RO flag.
* autoload.cc (WNetGetResourceInformationA): Import.
* fhandler_netdrive.cc (fhandler_netdrive::exists): Detect actual existence of
remote system rather than always assuming that it exists.