Change SCB_LIST_NULL to 0xff from 0x10 to allow for 255 commands.  This is needed for 3940 support.
Change SCB_LIST_NULL to 0xff from 0x10 to allow for 255 commands.  This
is needed for 3940 support.

Have tagged commands look to see if a target is "busy" with a non tagged
command before executing.  This prevents overlapped tagged and non tagged
commands which can happen since request sense commands are not tagged.

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