merged in changes from Ben to deal with Windows paths in r2stan_sys
merged in changes from Ben to deal with Windows paths in r2stan_sys

stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/math,stan-dev/stan,stan-dev/math,stan-dev/stan,stan-dev/math