Update CrashCatcher.h

* I moved the magic STACK_SENTINEL value into the public CrashCatcher
  header file so that CrashDebug wouldn't need to use the private
  header to check the last word in the dump to see if a stack overflow
  was detected.
* Added a CrashCatcherMemoryRegionInfo structure which is similar to
  CrashCatcherMemoryRegion except it doesn't have an elementSize
  field.  This is the structure used to actually describe each region
  in the dump itself as the elementSize has no meaning in the dumped
  data itself.  Everything is dumped as bytes in little endian order.
CrashCatcherDump.c should use CrashCatcherMemoryRegionInfo

The CrashCatcher dumps only include the starting and ending address for
each memory region.  The elementSize isn't used.  Previously the code
in CrashCatcherDump.c which read in the dump files incorrectly assumed
that the dumps did include this elementSize field.  I needed to fix
this incorrect assumption in the unit tests as well.
Now able to load CrashCatcher dumps in CrashDebug

I updated the CrashDebugCommandLine module so that it can now load dump
data obtained from CrashCatcher in addition to the GDB logs that it
previously supported.  There are no new command line flags.  The --dump
option still takes the name of the dump file and the module looks at
the file's signature to see which loader/parser should be used.