Refactorings to the filter code, most notably:
- Improve function name: parse_rule -> parse_filter_str (to make the
similarity with parse_filter_file clearer, and better indicate that
it can parse multiple rules when FILTRULE_WORD_SPLIT is specified).
- In preparation for rule prefixes containing information beyond the
rflags, change the code to pass around a full "template" filter_rule
instead of just rflags. Callers of parse_filter_{str,file} that want
to specify only rflags can use rule_template(rflags) .
- Remove the MODIFIERS_* strings and instead hand-code the condition
under which each modifier is valid. This should make it easier to
see that the conditions are correct.
- Tighten up default modifiers on merge rules:
- Disallow "!" because it isn't useful.
- If the merge rule specifies a side via "s" or "r", the rules in the
file cannot also specify a side via "s", "r", "hide", etc.
[Patch was changed by Wayne a bit prior to application.]