Added note about non-support of UNC paths on Windows.

This fixes SF bug #465447.

Doc/lib/libos.tex

@@ -634,7 +634,8 @@ Recursive directory creation function.  Like \function{mkdir()},
 but makes all intermediate-level directories needed to contain the
 leaf directory.  Throws an \exception{error} exception if the leaf
 directory already exists or cannot be created.  The default \var{mode}
-is \code{0777} (octal).
+is \code{0777} (octal).  This function does not properly handle UNC
+paths (only relevant on Windows systems).
 \versionadded{1.5.2}
 \end{funcdesc}
 

Doc/lib/libposixpath.tex

@@ -7,6 +7,10 @@
 This module implements some useful functions on pathnames.
 \index{path!operations}
 
+\strong{Warning:}  On Windows, many of these functions do not properly
+support UNC pathnames.  \function{splitunc()} and \function{ismount()}
+do handle them correctly.
+
 
 \begin{funcdesc}{abspath}{path}
 Return a normalized absolutized version of the pathname \var{path}.