allow name and description settings in doUpdateGroup

(fffb847) You can set 'name' and 'description' separately in doCreateGroup, but the corresponding code in doUpdateGroup is not available. Using the settings interface for these parameters seems to work.  Also, the prompt for illegal attributes was incorrect. Should say 'gam update group...', not 'gam create group...'

(c62fa88) Added another commit, because the doUpdateGroup sync function was not detecting existing group members correctly.