Merged changes from trunk

* r3908: expr docu update
* r3907: setpartab doc: added parameter convert in example
* r3906: expr: added support for operator ?:,&&,||
* r3905: gradsdes: removed support for option 360_day_calendar
* r3904: gradsdes: added support for option 360_day_calendar
* r3902: change cdi svn:external to tags/cdi-1.6.8
* r3901: expr: added support for operator ?: (short ifelse)
* r3900: eof, eofcoeff: docu update
* r3899: eof, eof3d: use area weights instead of no weights
* r3898: Vertstat cleanup
* r3897: Docu update
* r3896: Docu update
* r3895: vertmean, vertavg: changed to weighted means if layer bounds are available