[Carpet] using IO*::one_file_per_group

[Thomas Radke]

Hi,

various Carpet I/O thorns provide the feature of outputting all grid 
variables of a group into a single file, as opposed to the default of 
outputting each variable into a separate file.

It seems that at the moment one cannot have both: output of all 
variables from a group _and_ output of only a few selected variables 
from some other group. Wouldn't this feature be useful ?

-- 
Cheers, Thomas.