Bug fixes in tidal diagnostics.
Bug fixes in tidal diagnostics.

Remove check for 0 complex harmonic constituent when computing its phase
(complex argument) According to F2003 the results of atan2(0.,0.) is now well
defined (returning 0., other results may be obtained with atan2(+-0.,+-0.)) -
checked this for gfortran and ifort. This fixes bug #59.

Add halo update before FreeSurface is stored in FreeSurfaceHistory. Previously
I was seeing weird discontinuities across halo boundaries in the tidal diagnostics
this seems to fix it.

jjo31/ATHAM-Fluidity,rjferrier/fluidity,jrper/fluidity,rjferrier/fluidity,jrper/fluidity,rjferrier/fluidity,rjferrier/fluidity,iakovos-panourgias/fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,iakovos-panourgias/fluidity,jrper/fluidity,jjo31/ATHAM-Fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,rjferrier/fluidity,iakovos-panourgias/fluidity