Clean up test case for bug#14169

Temporarily commented out a query from the test case for bug 14169 to make it pass with --ps-protocol.

into  rurik.mysql.com:/home/igor/dev/mysql-4.1-2

into moonbone.local:/work/14169-bug-4.1-mysql

  Corrected test case for the bug#14169 to make it pass in --ps-protocol mode.

After a locking error the open table(s) were not fully
cleaned up for reuse. But they were put into the open table
cache even before the lock was tried. The next statement
reused the table(s) with a wrong lock type set up. This
tricked MyISAM into believing that it don't need to update
the table statistics. Hence CHECK TABLE reported a mismatch
of record count and table size.

Fortunately nothing worse has been detected yet. The effect
of the test case was that the insert worked on a read locked
table. (!)

I added a new function that clears the lock type from all
tables that were prepared for a lock. I call this function
when a lock failes.

No test case. One test would add 50 seconds to the
test suite. Another test requires file mode modifications.
I added a test script to the bug report. It contains three
cases for failing locks. All could reproduce a table
corruption. All are fixed by this patch.

This bug was not lock timeout specific.

The bug caused a reported index corruption in the cases when
key_cache_block_size was not a multiple of myisam_block_size,
e.g. when key_cache_block_size=1536 while myisam_block_size=1024.

into  mysql.com:/home/stewart/Documents/MySQL/4.1/merge

into  mysql.com:/home/stewart/Documents/MySQL/4.1/merge

into moonbone.local:/work/14169-bug-4.1-mysql

into  mysql.com:/usr/home/bar/mysql-4.1.b18691

into  april.(none):/home/svoj/devel/mysql/BUG17917/mysql-4.1

into  april.(none):/home/svoj/devel/mysql/BUG17917/mysql-4.1

Retrieving data from compressed MyISAM table which is bigger than 4G on 32-bit box
with mmap() support results in server crash.

mmap() accepts length of bytes to be mapped in second param, which is 32-bit
size_t. But we pass data_file_length, which is 64-bit my_off_t. As a result only
first data_file_length % 4G were mapped.

This fix adds additional condition for mmap() usage, that is use mmap() for
compressed table which size is no more than 4G on 32-bit platform.

Conversion from int and real numbers to UCS2 didn't work fine: 
CONVERT(100, CHAR(50) UNICODE)
CONVERT(103.9, CHAR(50) UNICODE)

The problem appeared because numbers have binary charset, so,
simple charset recast binary->ucs2 was performed
instead of real conversion.

Fixed to make numbers pretend to be non-binary.

used

In a simple queries a result of the GROUP_CONCAT() function was always of 
varchar type.
But if length of GROUP_CONCAT() result is greater than 512 chars and temporary
table is used during select then the result is converted to blob, due to
policy to not to store fields longer than 512 chars in tmp table as varchar
fields.

In order to provide consistent behaviour, result of GROUP_CONCAT() now
will always be converted to blob if it is longer than 512 chars.
Item_func_group_concat::field_type() is modified accordingly.

into  mysql.com:/home/mydev/mysql-4.1-bug5390

into  mysql.com:/home/mydev/mysql-4.1-bug5390

into  sanja.is.com.ua:/home/bell/mysql/bk/work-4.1

into  mysql.com:/usr/home/ram/work/mysql-4.1

into  sanja.is.com.ua:/home/bell/mysql/bk/work-4.0

into  mysql.com:/usr/home/ram/work/mysql-4.0

into  sanja.is.com.ua:/home/bell/mysql/bk/work-4.0

code. (Bug #13621)

into  mysql.com:/usr/local/mysql/mysql-4.1

into  perch.ndb.mysql.com:/home/jonas/src/mysql-4.1

into  mysql.com:/usr/local/mysql/mysql-4.1

into  mysql.com:/opt/local/work/mysql-4.1-16365

too many open statements". The patch adds a new global variable
@@max_prepared_stmt_count. This variable limits the total number
of prepared statements in the server. The default value of
@@max_prepared_stmt_count is 16382. 16382 small statements
(a select against 3 tables with GROUP, ORDER and LIMIT) consume 
100MB of RAM. Once this limit has been reached, the server will 
refuse to prepare a new statement and return ER_UNKNOWN_ERROR 
(unfortunately, we can't add new errors to 4.1 without breaking 5.0). The limit is changeable after startup
and can accept any value from 0 to 1 million. In case
the new value of the limit is less than the current
statement count, no new statements can be added, while the old
still can be used. Additionally, the current count of prepared 
statements is now available through a global read-only variable 
@@prepared_stmt_count.

into mysql.com:/M41/mtr-4.1

gives wrong results". Implement previously missing 
Item_row::cleanup. The bug is not repeatable in 5.0, probably 
due to a coincidence: the problem is present in 5.0 as well.