The fix for Bug 76611 caused ~20% performance loss in XLS import.
With optional cloning of ScTokenArray of the shared XLS formulas
depending on the need of address wrapping, it is possible to gain
back near the original performance.

Note: The original patch for Bug 76611 has already got an unit test,
too (see wrapped-refs.xls), and that unit test works with this
improved patch, too.

Change-Id: Ibfb59d1543ef9c4b8a075d5c4e37f77ab451aaa0