Dipole implementation in pswater potential for driver

[mahrossi]

PSwater potential now can pass the dipole moment to i-PI as well (through the driver interface). I also updated the pswater example since the water molecule there was split on the boundary of the box, which produced really strange results. Hope it is a quick merge.

Mariana

[mahrossi]

@grhawk : Just now noticed you have a branch expanding_driver. I guess I could have done this there. Hope it is easy to merge too? Cheers!

[ceriottm]

Just one thing: the water molecule being on the boundary seems to me the symptom more than the root cause: I think that one should fold the molecule around the oxygen before calling the pswater routines. Do you have time to implement that, or shall we just consider this as a quickfix rather than a proper solution?

[grhawk]

I think there will be no problems...

[mahrossi]

I guess I have time to implement that. Give me one more day :)

[mahrossi]

K done to cell center, could test the origin as it should be the same thing... trivial, it is now done anyway.

[mahrossi]

Can this be merged?