Applying autoupdate

[ClementPernet]

to update autotools scripts

[ClementPernet]

Applying the branch makes fflas-ffpack require autoconf v2.71 to be built from source tree. This is a much too recent version (e.g. not in Debian stable) to make the move now. In particular, we still want the CI slaves to build from upstream git master and the version requirement is too high for them.
As a consequence, let's put this branch on hold and consider merging it in the furure, when autoconf-2.71 will be largely distributed.