Removed limit of number of arguments passed to ``user add`` command.

This is needed as the ``user add`` command is supposed to accept a variable number
of arguments.
[#1425] Call logic.NotFound
Merge branch '1425-exception-fix'
Merge branch 'bug-1375-user-add-command-fix' of github.com:rshk/ckan into rshk-bug-1375-user-add-command-fix