Added automatic reconfigure

This should call ./configure again if ./configure itself has changed,
of if Makefile.conf.in has changed.

It should make more robust the switching between branches with
changes in these files.

The procedure has been adapteb from:
https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Automatic-Remaking.html#Automatic-Remaking