* automake.in: Don't declare TRUE and FALSE, import them from

* automake.in: Don't declare TRUE and FALSE, import them from
Automake::Conditional.
* lib/Automake/Conditional.pm (TRUE, FALSE): New constants.
(new): Simplify using FALSE.
(reduce): New function, moved from ...
* automake.in (variable_conditions_reduce): ... here.
(variable_conditions_recursive_sub, invert_conditions):
Adjust calls to Automake::Conditional::reduce.
* tests/cond12.test: Adjust to use Automake::Conditional.