prewalk and postwalk are use recursion in ways that will blow the stack for sufficiently deep nested structures.
I suggest that this be noted in various clojure.walk documentation strings since this kind of recursion/limit seems to be rare in Clojure, and hence will be unexpected.
(It'd be even better to remove the recursion/limit via something like zippers and iteration, but this issue is just a suggestion for improvement of the documentation.)
