This commit doesn't do any functional change to configure.ac but does a fair
amount of cleaning up.

It re-orders the various blocks by type (options, checks, expands, ...).
It also consistently uses tabs for indents.
Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>