Depending on tool versions used, "autoreconf -i" may not update all
Autoconf-generated files, which in turn may result in build errors.
Make autogen.sh call autoreconf with the "-f" command line argument to
ensure all Autoconf-generated files are updated when autogen.sh is run.
Signed-off-by: Emanuele Di Pascale <emanuele@voltanet.io>