Group item fields are implemented as varstrings nowadays.
Made init_connect.test robust against existing t1.


mysql-test/r/init_connect.result:
  Made init_connect.test robust against existing t1.
mysql-test/t/init_connect.test:
  Made init_connect.test robust against existing t1.
sql/sql_select.cc:
  Enlarged group item key_length by a varstring length field.
  Group item fields are implemented as varstrings nowadays.