(force_to_mode): Now pass actual AND mask instead of number off;

generalize appropriately.
Move most cases from simplify_and_const_int in.
(simplify_and_const_int): Remove most code from here; call force_to_mode
instead.
(subst, make_extraction, make_compound_operation): Change calls to
force_to_mode.
(make_field_assignment): Likewise.
(simplify_comparison): Add call to force_to_mode when doing a sign bit
comparison.

From-SVN: r5060