autoconf 2.70 migration
Arch linux is now shipping Autoconf 2.70, and this apparently causes multiple "obsolete" warnings in some macros (our own macros, as well some from the version of gnulib we ship). There is currently a gnulib macro (I believe) that seems to break configure with a unexpected newline, and causes two of our builds to fail.
- upgrade our copy of gnulib (preserving some of the argp fixes we use)
- try to reduce the amount of obsolete warnings, e.g. replacing AC_HELP_STRING by AS_HELP_STRING, as suggested.
Let's hope that the result can still work with Autoconf 2.69, which we can safely require. (If we need to require 2.70, it will be very painful.)
FWIW, Autoconf 2.70 is already packaged in Debian experimental.