Same sequence of Gaussian numbers with different compilers

This fixes #23
Notice that it slows down (with icpc) generation of Gaussian numbers
by a factor 2.5. I think it is better now to have reproducible regtests.
Fixed simplemd to write output file

It was a longstanding (unknown) bug!
I added reference output files for all the simpledmd
regtest. This will allow to distinguish bugs in plumed
from Lyapunov effects in trajectories.