automake 1.10 changed interpretation of AM_INIT_AUTOMAKE

[dherring]

I was just hit by a subtle bug; our configure.ac contained
AM_INIT_AUTOMAKE([-Wall -Werror foreign])
which, under 1.9.6 and earlier, effectively caught gmake-isms such as $%
and $(function ...).

People who upgraded to 1.10.1 started adding gmake-isms to Makefile.am.!. 
A little investigation finds that configure.ac now needs
AM_INIT_AUTOMAKE([foreign -Wall -Werror])
to maintain the old behavior.

I suspect that this is a bug in automake and that it was introduced around
1.10, based on this snippet from NEWS:
  - `-Wportability' has finally been turned on by default for `gnu' and
    `gnits' strictness.  This means, automake will complain about %-rules
    or $(GNU Make functions) unless you switch to `foreign' strictness or
    use `-Wno-portability'.

As a programmer, I realize that "apply settings in the order given" is a
simple, logical way to do things.  As a user, I don't think `foreign'
should silently disable the earlier, explicitly requested warnings.

Thanks,
Daniel