Rework the pre-trampoline code so that we always call the is_interesting_backtrace function.  So that I don't have to count hardcoded bytes, split up the code into separate groups where the end of each group is a dword immediate we'll be modifying.  Only update the main_caller_retaddr value when the depth count is 1.  This now works as expected in testing.  Also make sure that a deref of retaddr_esp never accesses out of bounds memory.