This removes the need to provide a separate source set for Clojure code
that the main source set depends on.

This may be related to #172, but doesn't test for Clojure depending on
Groovy/Kotlin/etc.

Porting the approach used to wire up the source from the Clojure
plugins. This is primarily for consistency, don't expect any
user-visible changes.

We need to ensure that the compile task was registered before we call
compiledBy on the SourceDirectorySet. This new ordering should be solid.

This was legacy from the way we generated templates. It could be
considered a breaking change for some if they relied on this, so should
document it if they still want it.

It seems I'm getting a wider exception in the Prepl input loop
sometimes, this AsynchronousCloseException instead of the
ClosedByInterrupteException (which is a subclass) we used to get and
were handling. This just caused some harmless, but confusing, stack
traces in the Gradle output. This change should help clean that up.

This removes special logic we had to disable Clojure tasks when the repl
was the only task requested at the command line. Instead, we're just
being more explicit about which stuff we put on the classpath, and avoid
having dependencies on any of the *classes tasks that pulled in all
language compile tasks.

The breaking change here is that compiled test Java classes will not be
on the classpath anymore, however that doesn't seem like a common need.

It will also be a little more fiddly to get other language classes on
the classpath, but won't be terrible.

This does revert b151ff1, so it will
require some other solution to allow you to get your ClojureScript
compiles on the classpath.

I think this involves outputting to build/tmp/clojureRepl, but need to
make that easier and let people get access to all of their build
configurations.