Almost exclusively this patch handled the addition of another char
array to the zfs_cmd_t structure. Unfortunately c90 doesn't allow
zero filling the entire struct with the '= { 0 };' shorthand.
Originally these changes were on other gcc-* topic branches but
because c90 touches the same bit of code and I'd like to keep all
the gcc-* branches completely parallel I've moved these few bits
over here. This is one of the downsides of not just having one
big patch stack.