Fix (seq {}) should be nil
Fix Cons is not counted and would be interpreted as an object

This is due to the cljs.core/count implementation first checking
for native-satisfies? and only then falling back to an
accumulating-seq-count.

Removing the protocol would use the accumulating-seq-count for
objects, which is somewhat slower.
Merge pull request #6 from deliminator/master

Fix (seq {}) and (count (cons ...))