For PR automake/353: fill %var_location, %var_comment,

For PR automake/353: fill %var_location, %var_comment,
%var_type, %var_owner for each condition.
* automake.in (msg_cond_var): New function.
(msg_var): Use it.
(generate_makefile, process_option_list, handle_languages,
handle_lib_objects_cond, handle_compile, handle_libtool,
handle_ltlibraries, handle_texinfo_helper, handle_tests,
handle_emacs_lisp, handle_python, macro_define, macro_delete,
macro_dump, variable_assert, variable_output,
variable_pretty_output, read_am_file, read_main_am_file,
file_contents_internal, am_primary_prefixes,
require_variables_for_macro): Adjust accesses to %var_location,
%var_comment, %var_type, %var_owner.
(append_comments, require_file_with_macro,
require_conf_file_with_macro, require_variables): Add the
$cond argument.
* tests/comment7.test: New file.
* tests/Makefile.am (TESTS): Add comment7.test.