Clears the overlay buffer.
Disposes of all currently loaded overlays from the overlay buffer. This forces subsequent calls to overlaid routines to reload the overlays from the overlay file (or from EMS). If OvrClearBuf is called from an overlay, that overlay will immediately be reloaded upon return from OvrClearBuf.
The overlay manager never requires you to call OvrClearBuf; in fact, doing so will decrease performance of your application, because it forces overlays to be reloaded. OvrClearBuf is solely intended for special use, such as temporarily reclaiming the memory occupied by the overlay buffer.