Bump nREPL dep to 0.2.4
Handle exceptions in test fixtures.

Better document the way the `test` middleware obtains line numbers for
erring tests.

Fixes CIDER #711.
Fix typo.
Limit the levels printed for exception data

When pprint'ing the exception data for an exception cause, limit the
depth of data printed to avoid errors on circular data structures.

Make the maximum printed level is configurable via the optional
print-level argument to the stacktrace op.  Defaults to 50.