This change is goes with cmGrFltk.cpp calls to cmGrDevCtxResize() which
now set the location as well as the size of the device context.

Added state[] variable to XFader DSP object.
Completed _cmDspSysPgm_AvailCh() example program.

Rewrote cmGr.c::cmGrEvent()
Callback cmGrIsInsideObj() now must evaluate both if the mouse point is
inside the object and also if the object can handle the event. This
allows the actual plot object which can handle an event to be identified
by cmGrEvent().

_cmGrPlotObjEvent() still needs to be updated to account for these changes.

The phasor value must be limited to a max value - the size of the wave table
otherwise the resolution of the phasor object phase counter eventually
diminishes due to the increasing value of the integer part of the
floating point value.  This will result in distortion in the wave table
output because the phase value will not increment reliably.

useThreadFl allows the background file loading thread to be enabled and disabled.