Better integration with swank-cdt

[tomfaulhaber]

(As discussed between myself and technomancy here: http://clojure-log.n01se.net/#12:21)

We should make it possible to invoke a clojure instance prepped for CDT without the user having to modify the project file. This could happen with a prefix argument to clojure-jack-in or maybe a related start function such as clojure-jack-in-debug.

There are three potential parts to this:

1. Add "-agentlib:jdwp=transport=dt_socket,server=y,suspend=n" to the Java options.
2. Add tools.jar and sa-jdi.jar from $(JAVA_HOME)/../lib to the classpath of the invoked JVM. (CDT tries to add these to the classpath with add-classpath, but doesn't always seem to succeed.)
3. Add a dependency to clojure-source.

Of these three, #1 is clearly required, #2 would make the whole structure more reliable, and I don't even know how we'd make #3 happen in the current structure (esp., since clojure-source doesn't seem to be pushed reliably).

We may want to do the underlying implementation a part of a new option to lein jack-in (e.g., "lein jack-in debug") so that it can be used by tools other than emacs, but that's obviously a matter for your judgment.

[tomfaulhaber]

One more suggestion that came from a conversation I had with George Jahad:

When you start a debug swank session with swank, pre-execute (use 'swank.cdt) so that the debugger commands are available right away from the slime repl.