STYLE: Add *.pyc files to .gitignore

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23394 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Restore original behavior of "Set(AndObserve)NthNodeReference" functions

This commit fixes test vtkSlicerUnitsLogicTest1 by partially reverting
commit r23192.

It restores the original behavior of the "Set(AndObserve)NthNodeReference"
functions. Instead of ensuring reference can be set and get at position
n, if n is larger than the number of reference nodes, the node ID
is added at the end of the list. If nodeReferenceID is 0, the node ID is
removed from the list.

Fixes #3708

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23395 3bd1e089-480b-0410-8dfb-8563597acbee