Pydev debugger and psyco speedups (target: 1.3.14)

The pydev debugger can now make use of psyco if it's available in the environment (it's actually highly recommended... in tests a 50% improvement in the debugger speed was observed... mainly, all the tracing goes through 2 functions, so, speeding it was pretty straightforward -- after discovering how to integrate it).

Now, this relation is kind of strange: the pydev debugger can make use of psyco, but the debugged code can't (because if it gets compiled, pydev can't trace it).

Until now, a Null() object was added as a psyco module in sys.modules so that clients didn't worry about it, but that had some nasty side effects, so, this version will also change this integration so that clients that rely on psyco don't have to change code: a stub module will replace the psyco module in sys.modules and will mimic it better -- and it'll be installed only after pydev finishes using it to get its optimizations.