yem/fixes: cleanups in configure.in

Hello!

Here is a small series to cleanup configure.in:
  - use the 'foreign' flag when initialising automake -> allows running 'autoreconf'
  - cleanup autogen.sh to just use autoreconf
  - rename configure.in -> configure.ac as per autoconf's manual

Being able to just use autoreconf instead of autogen.sh is very valuable for automated buildsystems, such as Buildroot (http://buildroot.org) which has an infrastructure to handle autotools-based packages.

Also, using autoreconf is the recommended (and the only supported way) to 'bootstrap' an autotools package. Calling each tool in sequence is long deprecated in favour of autoreconf, since it knows exactly what to do, in what order.

Regards,
Yann E. MORIN.