Patch #651006: Better explain what component might be empty.

Doc/lib/libposixpath.tex

@@ -123,7 +123,7 @@ Joins one or more path components intelligently.  If any component is
 an absolute path, all previous components are thrown away, and joining
 continues.  The return value is the concatenation of \var{path1}, and
 optionally \var{path2}, etc., with exactly one directory separator
-(\code{os.sep}) inserted between components, unless \var{path} is
+(\code{os.sep}) inserted between components, unless \var{path2} is
 empty.  Note that on Windows, since there is a current directory for
 each drive, \function{os.path.join("c:", "foo")} represents a path
 relative to the current directory on drive \file{C:} (\file{c:foo}), not