mysql-test/r/func_misc.result:
  Added test for Bug #21466: INET_ATON() returns signed int, not unsigned
mysql-test/t/func_misc.test:
  Added test for Bug #21466: INET_ATON() returns signed int, not unsigned
sql/item_func.h:
  Added unsigned_flag=1 value to Item_func_inet_aton.  
  This fixes bug #21466: INET_ATON() returns signed int, not unsigned