NPN driving PNP, Diode from NPN Base to PNP Collector?
I think it's short-circuit protection.  If the output is accidentally shorted to ground, D1 pulls the drive to the NPN down shutting the output off.  D2 is necessary since D1 can only pull the base down to a diode drop above ground, so D2 compensates the drop making Vbe (NPN) approximately zero.