added note about character set limitations in passwords.

Doc/lib/libnetrc.tex

@@ -59,3 +59,10 @@ as a pseudo-host by that name.
 \begin{memberdesc}{macros}
 Dictionary mapping macro names to string lists.
 \end{memberdesc}
+
+\note{Versions of this module before 2.2.3 and 2.3 are very limited to a
+subset of the ASCII character set for passwords.  Starting with 2.2.3 and
+2.3, ASCII punctuation is allowed in passwords.  However, note that spaces
+and non-printable characters are not allowed in passwords.  This is a
+limitation of the way the .netrc file is parsed and should be removed in the
+future.}