Moving to Autoconf 2.64, Automake 1.11

[Paolo Bonzini]

> - fix the (new with Autoconf 2.64) warnings from configure about unknown
>   --enable/--with switches.  I would appreciate some input on whether
>   this functionality should just be turned off with
>   AC_DISABLE_OPTION_CHECKING, or we should add some logic to the
>   toplevel configure script to be more intelligent about it.

For toplevel, add AC_DISABLE_OPTION_CHECKING definitely (at the same
time as the regeneration).

For other directories, we can decide later on a case-by-case basis.

Just for fun, if you have a diffstat of the world-regeneration, it would
be nice to see it.

Paolo