Handle unconditional values of variables as conditioned by

Handle unconditional values of variables as conditioned by
`TRUE'.
* automake.in (%contents): Remove.
(&generate_makefile, &handle_ltlibraries, &macro_define)
(&read_am_file, &variable_defined, &variable_conditions_sub)
(&variable_value, &variable_value_as_list_worker)
(&variable_value_as_list, &define_pretty_variable)
(&read_main_am_file): Use
$conditional, not %contents.
(&variable_conditions_permutations): Don't return TRUE and FALSE.
(&variable_conditionally_defined): New.
(&handle_dist): Use it.
(&check_ambiguous_conditional): When multiply defined, specify
under which condition.
(&macro_define): Use it.
(&variable_delete): New.
(&read_am_file): Use it.
(&am_install_var): Simplify, as all the variables are in
%conditional now.