* path.h: Create new input path flag PATH_NEEDDIR.

* path.cc (path::check): Detect trailing slash before converting to windows
path.  Tell symlink_info::check to check for directory if one is found.
(symlink_info::check): Set errno when path is not a directory if pflags &
PATH_NEEDDIR.

winsup/cygwin/path.h

@@ -36,6 +36,7 @@ enum path_types
   PATH_BINARY = MOUNT_BINARY,
   PATH_EXEC = MOUNT_EXEC,
   PATH_CYGWIN_EXEC = MOUNT_CYGWIN_EXEC,
+  PATH_NEEDDIR = 0x20000000,
   PATH_SOCKET =  0x40000000,
   PATH_HASACLS = 0x80000000
 };