New breakpoint tracking object. Keep track of breakpoints
and send Emacs only the deltas.
toolbox/emacsinit.m:
Initialize breakpoint tracker.
toolbox/ebstop.m, toolbox/ebclear.m, toolbox/ebstatus.m:
New wrappers for dbstop, dbclear, and dbstatus.
Calls the built-in, and then calls the breakpoint tracker
to tell emacs about any changes in breakpoints.