fix issue #4238- 'Save As on file in working set does not preserve working set order'

alternate fix for issue #4238 that replaces previously submitted pull request #4329 

The other pull request tries to more intelligently swap out the working set entries, but fails to open the newly saved document.  This approach leverages the already existing workflow in opening and adding the newly saved file to the working set.  However, rather than just appending the new file to the end of the working set list, the new code now supports an optional parameter which specifies where to insert it.  Consequently, we can insert the file into the same working order as it was before the file-save-as event.