BUG #14214: Miscellaneous fixes for tracing.

Cleaned up logic in tracing. We were ending up with out of order trace captures
resulting in broken trace files that didn't work as expected using all ParaView
executables. This was happening because a lot of new code added to smtrace
directly appended to the trace_output stream without flushing the information
currently gathered. Fixed that by streamlining the logic.

Also fixed a leak with trace observer. The observer was in place even after
tracing was stopped. Fixed that.

Change-Id: I805ffd7570c0b79ace9b540504a55c8f5e842b23
pqSMAdaptor not respecting unchecked flag.

pqSMAdaptor was not using unchecked set API for enumeration properties. Fixed
that.

Change-Id: I019f92da909b3bcdaef923f0ed40d930ee97eb74
Cleanup trace generated for Exodus reader.

Exodus reader was generating unnecessary entries in the trace file. This was
because the XML was setting a default number of values count for server
properties which wasnt needed. Fixed that.

Also fixed vtkSMVectorPropertyTemplate to fire modified event in SetElements(..)
for uninitialized properties only when the new value had a non-zero number of
elements.

Change-Id: Iab759d282e80e7818c67dbf8a002e8a37167b729
Fix python build dependency issue.

Certain targets were always dirty causing due to missing output file. Fixed
that.

Change-Id: I13616d14476bcca62b28e1d436934bacf561fa5e
Merge topic '0014214_fix_python_trace_issues'

f484146 Fix python build dependency issue.
f5e284d Cleanup trace generated for Exodus reader.
85dd5a3 pqSMAdaptor not respecting unchecked flag.
e48bf68 BUG #14214: Miscellaneous fixes for tracing.