* lib/Automake/Conditional.pm: New file.

* lib/Automake/Conditional.pm: New file.
* lib/Automake/Makefile.am (dist_perllib_DATA): Add Conditional.pm.
* automake.in: Use Automake::Conditional.
(TRUE, FALSE): New constants.
(%var_value, %var_location, %var_comment, %var_type, %var_owner,
%targets, %target_source, %target_name, %target_owner): Tie to
Tie::RefHash::Nestable.
(generate_makefile, process_option_list, handle_options,
handle_languages, handle_source_transform, handle_compile,
handle_libtool, handle_texinfo_helper, handle_dist, handle_subdirs,
scan_aclocal_m4, handle_emacs_lisp, handle_python,
scan_autoconf_files, variable_assert, define_variable,
define_pretty_variable, define_configure_variable, am_install_var,
push_dist_common): Use TRUE.
(define_objects_from_sources): Fix return value on
"recursively-defined" errors.
(conditional_string, conditional_true_when, conditional_is_redundant,
conditional_implies_any, make_conditions): Remove these functions,
obsoleted by Conditional.pm.
(cond_stack_if, cond_stack_else, cond_stack_endif): Return
an Automake::Conditional instance.
(by_condition, conditional_ambiguous_p,
variable_not_always_defined_in_cond, macro_define,
variable_conditions_recursive, variable_conditions_recursive_sub,
variable_conditions_reduce, invert_conditions,
variable_conditions_permutations,
check_variable_defined_unconditionally, variable_value_as_list,
variable_output, variable_pretty_output, rule_define,
read_am_file, file_contents_internal, require_variables): Adjust
to use Automake::Conditional objects.
(handle_footer): Get $(SUFFIXES) in 'all' conditions.
* tests/cond12.test: Adjust to use Automake::Conditional objects.