two new regtests for drift, I think they could be usefull for fix-241

regtest/basic/rt-drift-1/COLVAR.reference

regtest/basic/rt-drift-1/Makefile

regtest/basic/rt-drift-1/config

regtest/basic/rt-drift-1/eff.reference

regtest/basic/rt-drift-1/in

regtest/basic/rt-drift-1/input.xyz

regtest/basic/rt-drift-1/output.xyz.reference

regtest/basic/rt-drift-1/plumed.dat

regtest/basic/rt-drift-2/COLVAR.reference

regtest/basic/rt-drift-2/Makefile

regtest/basic/rt-drift-2/config

regtest/basic/rt-drift-2/eff.reference

regtest/basic/rt-drift-2/ff.0.reference

regtest/basic/rt-drift-2/ff.1.reference

regtest/basic/rt-drift-2/ff.2.reference

regtest/basic/rt-drift-2/ff.3.reference

regtest/basic/rt-drift-2/plumed.dat

regtest/basic/rt-drift-2/test.pdb

regtest/basic/rt-drift-2/trajectory.xyz

regtest/basic/rt-drift-3/COLVAR.reference