Fixed NetworkTables not calling NetworkTable::Shutdown() upon module unload

After extensive testing late last night and early this morning, I determined that the changes in this commit cause the FRC_UserProgram module to successfully unload and that a subsequent module load successfully completes (without crashes). I submitted it to FIRSTForge and am submitting it here because I've found being able to reload FRC_UserProgram.out without rebooting the cRIO to be very useful, albeit very few teams do it.