#3 indexing into multiple ParameterDef[]s with ParameterSet

[Matthew Weigel]

ParameterSet.indexDef() behaves incorrectly, in that it
recursively calls m_nextSet.indexDef() with the same
index - however, each ParameterDef[] will begin at index 0.

Fix: change line 99 from

return m_nextSet.indexDef(index);

to

return m_nextSet.indexDef(index - m_knownArguments.length);