Improved container trace variable semantics

[kpgriesser]

With the object tree we can print container elements (e.g. print Arr[5]) rather than cd Arr; print 5.
Can we support this for trace variables as well?
Here's an example of what we currently do for tracing multiple containers.

cd sst-ext-tests/tests/debug-console
sst --interactive-start=0s  dbgsst15.py
cd cp0
trace v_long changed : 8 4 : v_long : interactive
cd v_ag_struct
addTraceVar 0 0 1
cd ..
cd v_ag_class
addTraceVar 0 0 1
watchlist

  R0,T0: Current watch points:
  0: TriggerCount 0 : ALL : /cp0/v_long CHANGED  : bufsize = 8 postDelay = 4 : v_long 0 1 0 1  : interactive

With the object tree, could we support this?

cd cp0
addTraceVar v_long changed : 8 4 : v_ag_struct[0] v_ag_struct[1] v_ag_class[0] v_ag_class[1] : interactive

Better still:

addTraceVar cp0/v_long changed : 8 4 : cp0/v_ag_struct[0] cp0/v_ag_struct[1] cp0/v_ag_class[0] cp0/v_ag_class[1] : interactive