BUG#9998 MySQL client hangs on "USE database"

Use open_normal_and_derived_tables instead of open_and_lock_tables when reading metadata for a table.
 Add two test cases, one for "USE database" and one for "SHOW COLUMNS FROM table"


mysql-test/r/lock_multi.result:
  Updated test results for test case for bug9998
mysql-test/r/mysql.result:
  Updated results for test case for bug9998
mysql-test/t/lock_multi.test:
  Test that "show columsn from t1" is not locked by another thread having a write lock on t1
mysql-test/t/mysql.test:
  Add test case for BUG9998
    - lock table t1 for write from mysql-test, then execute 'mysql' and call "USE test". This will test exactly what caused the bug.
sql/sql_show.cc:
  Open tables without locking when reading metadata

mysql-test/r/lock_multi.result

@@ -36,3 +36,10 @@ lock table t1 write, t2 write;
 drop table t2;
 ERROR 42S02: Table 'test.t2' doesn't exist
 drop table t1;
+create table t1(a int);
+lock tables t1 write;
+show columns from t1;
+Field	Type	Null	Key	Default	Extra
+a	int(11)	YES		NULL	
+unlock tables;
+drop table t1;

mysql-test/r/mysql.result

@@ -48,3 +48,9 @@ Test  'go' command g
 a
 1
 drop table t1;
+create table t1(a int);
+lock tables t1 write;
+database()
+test
+unlock tables;
+drop table t1;

mysql-test/t/lock_multi.test

@@ -94,3 +94,15 @@ connection reader;
 reap;
 connection locker;
 drop table t1;
+
+
+#
+# BUG#9998 - MySQL client hangs on USE "database"
+
+create table t1(a int);
+lock tables t1 write;
+connection reader;
+show columns from t1;
+connection locker;
+unlock tables;
+drop table t1;

mysql-test/t/mysql.test

@@ -30,5 +30,14 @@ select "Test 'go' command(vertical output) \G" as " ";
 select "Test  'go' command \g" as " ";
 --exec $MYSQL test -e 'select * from t1\g'
 --enable_query_log
-
 drop table t1;
+
+#
+# BUG9998 - MySQL client hangs on USE "database"
+#
+create table t1(a int);
+lock tables t1 write;
+--exec $MYSQL -e 'use test; select database();'
+unlock tables;
+drop table t1;
+