#3 bug with PRIO_RULE support in v 0.8.5

[Oleksandr Darchuk]

In v 0.8.5 support for PRIO_RULE was added. But when
insert this parameter in class file it does'nt effect.
That's because of mistake in function s
htb_filter_file: regular expression that match string
before "=" in class file is " ^[a-zA-Z0-9]+". But
PRIO_RULE doesn't match it because of "_" sign. Change
part of regexp to "^[a-zA-Z0-9_]+" (add _ in brackets)
and everything works fine.