Fixed do_then, do_else, do_then_else operators
OperatorsSuite now handles VM exceptions
SimpleScriptDebugger: improved output options
~~>, ~~>...~/~> and ~/~> expressions now parsed well.
Rudimentary translation to do_then etc.
Work in progress: adding support for script result values.

This commit does NOT compile, mainly since generated code for scripts lack actual type parameters for references to T_call and N_call.

For an indication of how that problem could or should be solved see the comment in Typers.scala that was added in this commit.
"ant quick.subscript" on this commit will create a working compiler, but due to compile errors no VM is created.
To help overcome that, the "_dataflow" methods in DSL have been outcommented, since these contain anonymous scripts (that cannot be compiled yet).

When all sources containing script definitions have been moved away (akka, examples, Predef, swing.Scripts, GraphicalDebugger, OperatorsSuite etc(?)),
the VM classes should compile. When trying to get all scripts compiling well again, you could start with bringing Predef back in the scope of the ant command.