back referential expressions can cause exponential compilation times

Reported as causing problems in real world code: https://groups.google.com/forum/#!topic/clojure/Z91bhUvSB1g

With init.clj as :

Before patch:

After patch:

This is caused by every local bindings' type depending on the type of the previous binding, triggering an exponential number of calls to hasJavaClass and getJavaClass. By caching on first occurrence, the complexity becomes linear.

Patch: 0001-CLJ-2210-cache-non-trivial-getJavaClass-hasJavaClass.patch

Prescreened by: Alex Miller