Add zahir (AIX) in libIGCM scripts

zahir is the scalar MPP computer at IDRIS. ​http://www.idris.fr/su/Scalaire/zahir/index.html

The OS on next scalar MPP at IDRIS will be the same on Power 6. We need to prepare IPSLCM4/5 portability on Power6 and porting libIGCM on zahir is a prerequisite.

Add/Modify? histday and histhf to fill ensembles variables without too much post-processing ​http://www.mad.zmaw.de/projects-at-md/ensembles/output-variables/

OPA compilation : comopa common size warning

A warning message appears : sxld warning: multiply defined symbol comopa_, in ../../../lib/libopa.a, has more than one size

This COMMON appears in redrunnc.F and savrunnc.F with zdept(1)

      REAL zdtsec
      REAL zdept(1), zlamt(imax,jmax), zphit(imax,jmax)
      COMMON /comopa/zdtsec, zlamt, zphit,zdept

and with ztmask(imax,jmax) elsewhere :

      REAL zglamt(imax,jmax),zgphit(imax,jmax),ztmask(imax,jmax)
      COMMON /comopa/zdtsec,zglamt,zgphit,ztmask