Correction of stepToReturn command to be able to step to non-local returns.

[adri09070]

Fixes #21
In SindarinDebugger, the stepToReturn command didn't step to returns in blocks, as its implementation was using stepOver.

I've tried an implementation that uses stepThrough, which indeed fixed the problem, but that is problematic as stepThrough actually steps beyond exception signals if these exceptions are resumable.

I've also tried an implementation that uses stepInto, which also fixed the problem, but that is problematic as stepInto stops on halts, which is not the expected behaviour.

Now, the implementation I've done matches all 3 goals:
While a return hasn't been reached in the lexical context or an exception hasn't been signaled, we stepOver (to step on exceptions but not halts) except if we are on a message node that has, as a receiver or as an argument, a block that is defined in the same lexical context in which we step to return. In the latter case, we stepInto to enter the block.

Furthermore, SindarinDebugger >> hasSignalledUnhandledException has been modifed as it actually has never worked before to stop on exception signals. Indeed, the Sindarin>>testStepToReturnWithException was stopping correctly "by chance" on theexception signal because the current context, which is the context of the exception, returned.

Now, SindarinDebugger >> hasSignalledUnhandledException actually causes stepToreturn to stop on exception signals.