[ecj] Improved VMStackWalker.getCallingClass()

[Gary Benson]

Andrew Haley wrote:
> Gary Benson writes:
> > This commit makes VMStackWalker.getCallingClass() unwind only
> > as much of the stack as it needs in the cases when it has to.
> 
> Very good, thanks.
> 
> Is that the last part of your VMStackWalker work?

VMStackWalker.getCallingClassLoader() unwinds the full stack in
some circumstances and I'd like to give it the same treatment.
Other than that, yes.

Cheers,
Gary