* scripts/autotools-install: Increase automake's version number
to 1.15 and add Stefano Lattarini's new GPG key ID.
Increase gettext's version to 0.19.4 and add Daiki Ueno's GPG key ID.
Also move VERSION definition "up" so that it is once again
automatically updated via the emacs hook snippet at the end
of the file.
* scripts/autotools-install (tarballs): Use http:// URLs rather
than ftp:// ones. The former are more likely to work, these days.
Update URLs to point to the latest versions.
* scripts/autotools-install: Honor $MAKE. This might be useful
on systems where the make implementation available in $PATH
by default is limited (Solaris) or broken (HP-UX).
* scripts/autotools-install: New script, so you can always build
from git-cloned sources, even when they require bleeding edge
m4, autoconf, automake, etc.
