PATCH to top level: don't use dirname in configure

[Eli Zaretskii]

> Date: Fri, 21 Jul 00 17:29:14 CDT
> From: msokolov@ivan.Harhan.ORG (Michael Sokolov)
> 
> ! topsrcdir=`cd \`echo ${progname} | sed 's:/configure$::'\`; pwd`

This assumes that (a) $(progname) always expands to "configure", and
(b) that the last delimiter is '/'.  I don't know whether the first
assumption is true on each supported system, but the second might be
wrong on DOS/Windows where a backslash might be used instead.

In contrast, `dirname' (when it exists) will always DTRT, because it
is tailored to the host system.