Added note about non-support of UNC paths on Windows.
This fixes SF bug #465447.
diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index 1c3a584..85355a5 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -634,7 +634,8 @@
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}