Fixes for mysql-test failures

mysql-test/r/acl_roles_show_grants.result:
  one can do SHOW GRANTS for himself
mysql-test/t/acl_roles_set_role-table-column-priv.test:
  correct error message
mysql-test/t/acl_roles_show_grants.test:
  one can SHOW GRANTS for himself
sql/sql_acl.cc:
  bugfixing:
  * don't assign with && - it can shortcut and the second assignment won't be executed
  * correct the test in check_grant_all_columns() - want_access should not be modified
  *
sql/sql_cmd.h.OTHER:
  add new commands at the end
sql/sql_db.cc:
  don't call acl_get() if all privileges are already satisfied
  (crashes when run with --skip-grants, because acl data stuctures aren't initialized)
sql/sql_parse.cc:
  * test for current_user in get_current_user()
  * map explicitly specified user@host to current_user

mysql-test/suite/funcs_1/r/is_tables_mysql.result

@@ -428,6 +428,29 @@ user_comment	User proxy privileges
 Separator	-----------------------------------------------------
 TABLE_CATALOG	def
 TABLE_SCHEMA	mysql
+TABLE_NAME	roles_mapping
+TABLE_TYPE	BASE TABLE
+ENGINE	MYISAM_OR_MARIA
+VERSION	10
+ROW_FORMAT	Fixed
+TABLE_ROWS	#TBLR#
+AVG_ROW_LENGTH	#ARL#
+DATA_LENGTH	#DL#
+MAX_DATA_LENGTH	#MDL#
+INDEX_LENGTH	#IL#
+DATA_FREE	#DF#
+AUTO_INCREMENT	NULL
+CREATE_TIME	#CRT#
+UPDATE_TIME	#UT#
+CHECK_TIME	#CT#
+TABLE_COLLATION	latin1_swedish_ci
+CHECKSUM	NULL
+CREATE_OPTIONS	#CO#
+TABLE_COMMENT	#TC#
+user_comment	
+Separator	-----------------------------------------------------
+TABLE_CATALOG	def
+TABLE_SCHEMA	mysql
 TABLE_NAME	servers
 TABLE_TYPE	BASE TABLE
 ENGINE	MYISAM_OR_MARIA