If the line never changes during execution, the line step won't actually finish.
2006-11-11 Mike Cvet <firstname.lastname@example.org>
* SourceWindow.java (lineLoopCount): Added. Keeps track of the
number of instructions executed by each thread.
(stepIn): If lineLoopCount reaches a certain level, we should assume
that the line just won't change, and re-block everything.
(updateShownStackFrame): If the selected frame has line number equal
to zero, don't do anything.