Add loop function in cgen/arr in preparation for refactoring.
Move common checks out of loop in cgen/arr.
Switch input from arities to sequences.
Split out loop and rename it cgen/seq.
Make cgen/seq take its args in the correct order.
Cleanup some cases of cgen/seq.
Make value inference just delegate to sequence logic.
Make dotted functions of the same bound correctly be inferred.
Fix uniform arg checking, and minor cleanup.
Fix dotted <: starred case.
Make list inference code be shared with sequence code.
Merge case for applying polydotted functions.
Split out shared code for generating dbound prefixes.