add warning about ":" in directory names

[Paul Eggert]

I installed this:

2006-06-01  Paul Eggert  <address@hidden>

        * doc/autoconf.texi (File System Conventions): Warn about ":"
        anywhere in directory names.

--- doc/autoconf.texi   31 May 2006 20:20:13 -0000      1.1032
+++ doc/autoconf.texi   1 Jun 2006 07:47:24 -0000
@@ -10947,7 +10947,9 @@ the following:
 
 Also, file names should not begin with @samp{~} or @samp{-}, and should
 contain neither @samp{-} immediately after @samp{/} nor @samp{~}
-immediately after @samp{:}.
+immediately after @samp{:}.  On Posix-like platforms, directory names
+should not contain @samp{:}, as this runs afoul of @samp{:} used as the
+path separator.
 
 These restrictions apply not only to the files that you distribute, but
 also to the absolute file names of your source, build, and destination