LVDIFF 7.1.1 upload by user

The Compare 2 VIS.vi was changed from LV7.1 to LV8.x. The LVDIFF program calls this be reference from the location in the labview libraries. As such the reference to the different version is broken. I have simply added a reference for the missing version, and slightly modified the code so that it'd run.

This is only the lvdiff.vi, not any of the other materials from the .zip file that can be downloaded from the project.