This is the rev 502 of the Snowball SVN trunk,
made abstract and introduced abstract method stem to avoid expensive reflection in filter class.
refactored StringBuffers to StringBuilder
uses char as buffer instead of StringBuffer/StringBuilder
eq_s,eq_s_b,insert,replace_s take CharSequence like eq_v and eq_v_b
reflection calls (Lovins, etc) use EMPTY_ARGS/EMPTY_PARAMS