Given a function with one fixed argument and a vararg, it should be sufficient to force evaluation of 2 elements for apply to know which arity it should select, however it currently forces 3:
`
user=> (defn x ([a & b]))
'user/x
user=> (apply x (map println (iterate inc 0)))
0
1
2
nil
`
This makes lazy functions that use apply (for example mapcat) less lazy than they could be.
The proposed patch makes RT.boundedLength short-circuit immediately after the seq count is greater than the max fixed arity:
`
user=> (defn x ([a & b]))
'user/x
user=> (apply x (map println (iterate inc 0)))
0
1
nil
`
