This changes the LOG macro to be varadic removing the need for all
callsites to have double bracketing and allows for future improvement
on how we use the logging macros.
The callsites were changed with coccinelle and the changes checked by
hand. Compile tested for several frontends but not all.
A formatting annotation has also been added which allows the compiler
to check the parameters and types passed to the logging.
Remove all references to gui_current_drag_type outside of gui.c which are not related to routing DataSaveAck messages.
Update button bar drag code so that it uses ro_mouse.
