Made code compile on OSX

src/BaseGrid.h

src/BrownianParticleType.h

src/ComputeForce.h

src/DcdWriter.h

src/FlowForce.h

src/GrandBrownTown.h

src/Makefile

src/RandomCUDA.cu

src/RigidBodyGrid.h

src/Scatter.h

src/arbd.cpp

src/findcudalib.mk

src/gridSampleDef.c

src/gridSampleFlow.c

src/useful.h