Display compiler's error location in stacktrace.

`clojure.lang.Compiler$CompilerException`s carry the reader location of
the error, but not much else. Display the compiler exception's
location description (when present); then show the details from its
original cause.
Yeah. That function moves point and returns it, if a next cause exists. If you know of succinct a way to express the same thing that is somehow clearer, I'd be happy to use that.