Now crashed when wrong keywords are used in COORDINATION SWITCH=...

when a domain of domain decomposition is empty.

The fix to #39 was incorrect since adding an int to a string
does not print it.

I also removed the redundant check that index is positive (it is unsigned)

Check for NULL pointers is postponed to class Atoms and is done only if
there are local atoms. This fixes the case where GROMACS put zero atoms in
 a processor and assign a NULL pointer to positions

doesn't have this keyword

(cherry picked from commit 57c32f90)

I removed an assert and added an if then plumed_merror

close #39

I fixed the usage of stopflag in driver so that it is clearer
that the program stops at the end of the present step and not
at the beginning of the following. This is obviously equivalent,
but shows that scope of the flag can be reduced to be defined
at the inner of the MD loop.

Even if this is not a bux fix, I consider it as paired with fix #47
and I merge it to v2.0

(should be checked by GT)

This test shows a problem in reweighting (discussed in #48).
In particular, histoA and histoB in this regtest should not
come out identical as they do.

I think this is more coherent with other cmd() calls.

The interface to set replica communicator from fortran was missing.

It just prints a meaningful error.

file the residues they use.

To be consistent with the paper, plumed is always capital letters.
I also changed 2.0 -> 2 and 1.0 -> 1 for sake of generality

Without STORE_GRIDS it is necessary to flush the grid file,
otherwise it might stay empty for the entire simulation

When not RESTARTing:
file is backed up if existing.
  with STORE_GRIDS, file grows during simulation
  without STORE_GRIDS, file is replaced every time grid is rewritten

When RESTARTing:
  with STORE_GRIDS, file is appended and grows during simulation
  without STORE_GRIDS, file is replaced every time grid is rewritten

This hopefully fixes #34