Made user_limits.test scheduling independant (this solves failure on QNX).

Made sys_var_max_user_conn variable int sized. Changed 
max_user_connections from ulong to uint to be able to use it in 
sys_var_max_user_conn::value_ptr() (solves failures on 64-bit platforms).


mysql-test/r/user_limits.result:
  Made test scheduling independant.
mysql-test/t/user_limits.test:
  Made test scheduling independant.
sql/mysql_priv.h:
  Made max_user_connections to be the same size as
  USER_RESOURCES::user_conn (to be able to use them in
  sys_var_max_user_conn::value_ptr()).
sql/mysqld.cc:
  Made max_user_connections to be the same size as
  USER_RESOURCES::user_conn (to be able to use them in
  sys_var_max_user_conn::value_ptr()).
sql/set_var.cc:
  sys_var::item():
    Added support for int system variables.
sql/set_var.h:
  Made sys_var_max_user_conn to be int sized variable.