Restore SI_SUB_MOUNT_ROOT.  It was removed in an unrelated change on HEAD that has not been MFC'd.
Restore SI_SUB_MOUNT_ROOT.  It was removed in an unrelated change on HEAD
that has not been MFC'd.

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase