[patch libiberty include]: Add additional helper functions for directory-separator searching

[Eli Zaretskii]

> Date: Tue, 8 Mar 2011 16:29:51 +0100
> From: Kai Tietz <ktietz70@googlemail.com>
> 
> Umm, sorry. I found a wrong copy & paste. So I re-sent the corrected
> patch. Additionally I adjuste the changes in Makefile.in so, that
> alphabetic order remains.

I think we don't need filename_dirchr, only filename_dirrchr.

And you didn't change anything in the documentation to address my
comments earlier today.