Major Description
Tokenizers/Filters can now produce graphs instead of a single linear
chain of tokens, by setting the PositionLengthAttribute, expressing
where (how many positions ahead) this token "ends".
The default is 1, meaning it ends at the next position, to be
backwards compatible.
SynonymFilter produces graph output tokens, as long as the output is a
single token, but currently never sets the pos length to express this.
EG for the rule "wifi network -> hotspot", the hotspot token should
have pos length = 2. With LUCENE-3940 this will allow us to verify
that the offsets for such tokens are correct...