COMP: Fix sign-compare warnings in FiberTractMeasurements

This commit fixes the sign-compare warning reported below and also use
vtkIdType where it applies.

// ---------
/path/to/Slicer/Modules/CLI/FiberTractMeasurements/FiberTractMeasurements.cxx:208:45: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for (int o=0; o<operations.size(); o++)
^
/path/to/Slicer/Modules/CLI/FiberTractMeasurements/FiberTractMeasurements.cxx:223:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for (int i=0; i<fiberNodes.size(); i++)
^
/path/to/Slicer/Modules/CLI/FiberTractMeasurements/FiberTractMeasurements.cxx:232:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for (int o=0; o<operations.size(); o++)
^
/path/to/Slicer/Modules/CLI/FiberTractMeasurements/FiberTractMeasurements.cxx:280:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for (int o=0; o<operations.size(); o++)
^
/path/to/Slicer/Modules/CLI/FiberTractMeasurements/FiberTractMeasurements.cxx:306:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for (int o=0; o<operations.size(); o++)
^
// ---------

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23902 3bd1e089-480b-0410-8dfb-8563597acbee