Fix minimum value of query_prealloc_size to be the same as its default. (Bug #13334)

mysql-test/r/variables.result:
  Add new results
mysql-test/t/variables.test:
  Add new regression test
sql/mysqld.cc:
  Fix minimum value of query_prealloc_size to be the same as its default.

mysql-test/r/variables.result

@@ -499,3 +499,8 @@ set names latin1;
 select @@have_innodb;
 @@have_innodb
 #
+set @test = @@query_prealloc_size;
+set @@query_prealloc_size = @test;
+select @@query_prealloc_size = @test;
+@@query_prealloc_size = @test
+1

mysql-test/t/variables.test

@@ -388,7 +388,6 @@ set character_set_results=NULL;
 select ifnull(@@character_set_results,"really null");
 set names latin1;
 
-# End of 4.1 tests
 
 #
 # Bug #9613: @@have_innodb
@@ -396,3 +395,12 @@ set names latin1;
 
 --replace_column 1 #
 select @@have_innodb;
+
+#
+# Bug #13334: query_prealloc_size default less than minimum
+#
+set @test = @@query_prealloc_size;
+set @@query_prealloc_size = @test;
+select @@query_prealloc_size = @test;
+
+# End of 4.1 tests

sql/mysqld.cc

@@ -5280,7 +5280,8 @@ The minimum value for this variable is 4096.",
    "Persistent buffer for query parsing and execution",
    (gptr*) &global_system_variables.query_prealloc_size,
    (gptr*) &max_system_variables.query_prealloc_size, 0, GET_ULONG,
-   REQUIRED_ARG, QUERY_ALLOC_PREALLOC_SIZE, 16384, ~0L, 0, 1024, 0},
+   REQUIRED_ARG, QUERY_ALLOC_PREALLOC_SIZE, QUERY_ALLOC_PREALLOC_SIZE,
+   ~0L, 0, 1024, 0},
   {"range_alloc_block_size", OPT_RANGE_ALLOC_BLOCK_SIZE,
    "Allocation block size for storing ranges during optimization",
    (gptr*) &global_system_variables.range_alloc_block_size,