Re: gnulib-tool.py: Locate configure.ac correctly when --dir is given.

[Bruno Haible]

Hi Collin,

> When running ./autogen.sh in gettext gnulib-tool.py fails on the first
> invocation. :(
> 
> The command is something like this:
> 
>     $GNULIB_TOOL --dir=gettext-runtime ...
> 
> We get the following error message:
> ...
> FileNotFoundError: [Errno 2] No such file or directory: 
> 'gettext-runtime/gettext-runtime/configure.ac'
> ...
> In main we have joinpath(destdir, 'configure.ac') which is then passed
> to GLConfig.setAutoconfFile which has
> os.path.join(self.table['destdir'], configure_ac).

And in particular, main.py tests whether the file actually exists; therefore
GLConfig *must* just accept the string as it is, without making modifications
to it.

Thanks for the patch; applied.

Bruno