* Introduced a new function CaptureBacktrace, using it to handle most of back-tracing in heaptrc unit.
* Use StackTop instead of StackBottom+StackLength in a few remaining locations.


git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@27141 3ad0048d-3df7-0310-abae-a5850022a9f2