Added ability to specify system type/revision in config file. This

Added ability to specify system type/revision in config file. This
way a Tru64 system can be either Tlaser (by default) or Tsunami.

Added debugSymbolTable to Tru64 for symbol printing in InstExec Trace

cpu/exetrace.cc:
    Fixed bug if debugSymbolTable doesn't exist, we shouldn't try to
    look something up in it.
kern/tru64/tru64_system.hh:
    Added ability to specify system type/revision in config file. This
    way a Tru64 system can be either Tlaser (by default) or Tsunami.

--HG--
extra : convert_revision : c69a7411f0aa118ca5a766e43b7ceb7a5bb04cdf