Update junit plugin.

This is a port of changes from
https://github.com/josephwilk/midje-junit-formatter/pull/1.
Thus:
1. the junit plugin now reports testcase run times.
  No test suite execution times are included, though.
2. generated xml is `mvn surefire-report`-compatible
  i.e. the testsuite elements have a `name` attribute
3. it should be a bit easier to use the junit plugin with clojure.test
Revert a breaking change.

Apparently it's only within a midje.* namespaces that calling
xml emit on a failure result causes a stack overflow.
Add a 'junit-with-default' emission plugin.

It creates both the junit reports and the default stdout.
Merge pull request #237 from JacekLach/junit-surefire-compatibility

JUnit output breaks compatiblity (`deftest`-wrapped) forms executed via `lein test`