* automake.in (&macro_define): Don't lose the location if we

* automake.in (&macro_define): Don't lose the location if we
redefine a variable.
Don't push all the variables in @var_list, let...
(&read_am_file, &file_contents): ... do it.
(&define_pretty_variable): Use macro_define.
(&am_install_var): Delete the value of variables being redefined
to pacify &macro_define which checks that variables are not
doubly defined.