Add classnames of exceptions

[joegallo]

I'm not sure if this is desirable, but I've been having trouble with the exceptions I've been getting from lein-difftest, and I think I tracked it back to clj-stacktrace.

Without my changes, the behavior looks like this:
user=> (use 'clj-stacktrace.repl)
nil
user=> (pst (RuntimeException. "foo" (RuntimeException. "bar")))
foo
NO_SOURCE_FILE:4 user/eval134
Compiler.java:5424 clojure.lang.Compiler.eval
Compiler.java:5391 clojure.lang.Compiler.eval
core.clj:2382 clojure.core/eval
main.clj:183 clojure.main/repl[fn]
main.clj:204 clojure.main/repl[fn]
main.clj:204 clojure.main/repl
RestFn.java:422 clojure.lang.RestFn.invoke
NO_SOURCE_FILE:1 user/eval13[fn]
AFn.java:24 clojure.lang.AFn.run
Thread.java:662 java.lang.Thread.run
Caused by: bar
nil

With my changes, the behavior looks like this:
user=> (use 'clj-stacktrace.repl)
nil
user=> (pst (RuntimeException. "foo" (RuntimeException. "bar")))
java.lang.RuntimeException: foo
NO_SOURCE_FILE:4 user/eval136
Compiler.java:5424 clojure.lang.Compiler.eval
Compiler.java:5391 clojure.lang.Compiler.eval
core.clj:2382 clojure.core/eval
main.clj:183 clojure.main/repl[fn]
main.clj:204 clojure.main/repl[fn]
main.clj:204 clojure.main/repl
RestFn.java:422 clojure.lang.RestFn.invoke
NO_SOURCE_FILE:1 user/eval13[fn]
AFn.java:24 clojure.lang.AFn.run
Thread.java:662 java.lang.Thread.run
Caused by: java.lang.RuntimeException: bar
nil
user=>

I'm not entirely sure I understand where things went wrong, as it looks in the README like the classnames are supposed to be there to begin with, but I haven't been able to get clj-stacktrace to give me them.

Feel free to point out if I've misunderstood something, or if you have any criticism.

Side note to Mark: I met you briefly at the conj, and enjoyed your talk.

[mmcgrana]

Yeah, looks like class names got lost at some point. I need to get a chunk of time to dig into the details, but barring any surprises I should get this merged soon.