update AGNI potential for Al, reference runs and output and citation

examples/USER/misc/agni/Al_jpc.agni

examples/USER/misc/agni/Al_prb.agni

examples/USER/misc/agni/in.adatom

examples/USER/misc/agni/in.vacancy

examples/USER/misc/agni/log.21Feb17.adatom.g++.1

examples/USER/misc/agni/log.21Feb17.adatom.g++.4

examples/USER/misc/agni/log.21Feb17.vacancy.g++.1

examples/USER/misc/agni/log.21Feb17.vacancy.g++.4

potentials/Al_jpc.agni

potentials/Al_prb.agni

src/USER-MISC/pair_agni.cpp