R: [Gdal-dev] GNU make build system update

[Amici Alessandro]

Frank,

> I suppose we should upgrade. I see I have autoconf 2.53 here on my redhat
> system, so something around that version should be fine.

ok. the latest autoconf release, namely 2.57, is the default on both
platforms
i have access to: debian (unstable) and cygwin. i vote for that.

so i will commit the needed changes and the configure script built with 
autoconf 2.57 later.

cheers,
alessandro