really damaged MyISAM tables

When unpacking a blob column from broken row server crash
could happen. This could rather happen when trying to repair
a table using either REPAIR TABLE or myisamchk, though it
also could happend when trying to access broken row using
other SQL statements like SELECT if table is not marked as
crashed.

Fixed ulong overflow when trying to extract blob from
broken row.

Affects MyISAM only.

After merge fix.

After merge fix

After merge fix

Fixed a possible problem with reading of dynamic records
when a write cache is active. The cache must be flushed
whenever a part of the file in the write cache is to be 
read.

Added a read optimization to _mi_read_dynamic_record().

No test case. This was a hypothetical but existing problem.

A corrupt table with dynamic record format can crash the 
server when trying to select from it.
        
I fixed the crash that resulted from the particular type 
of corruption that has been reported for this bug.

No test case. To test it, one needs a table with a very special
corruption. The bug report contains a file with such a table.

myisam_max_extra_sort_file_size is depricated
Ensure that myisam_data_pointer_size is honoured when creating new MyISAM files
Changed default value of myisam_data_pointer_size from 4 to 6 to get rid of 'table-is-full' errors

Add support for VARCHAR with 1 or 2 length bytes
Enable VARCHAR packing in MyISAM files (previous patch didn't pack data properly)
Give error if we got problems in temporary tables during a SELECT
Don't use new table generated by ALTER TABLE if index generation fails
Fixed wrong call by range_end() (Could cause an ASSERT in debug mode)

some reason wasn't included before.
A lot of files cleaned up from #include <assert.h>

Add pack_bits to pack_reclength for dynamic rows.  This solves buffer a possible buffer overflow on update.
(This will probably solve bug #563)
Fix test for available file descriptors in mysqltest
Fixed core dump bug in replication tests when running without transactional table support

Better fix for format('nan')
Fix for HAVING COUNT(DISTINCT...)

least one BLOB column.

many NULL columns.

It could be ported back to 3.23 too ....

Fixed some windows portability problems and removed some compiler warnings
 Cleaned up QUOTE() function and fixed bug in \0 and \Z handling.

Fixed bugfix of INSERT ... SET db_name.table_name.column_name
Changed locking to external-locking
Fix client hangup for some invalid SQL queries.

This fixes that mysamchk --sort-records works on windows.

Fixed memory leak on shutdown (Affects the embedded version & MyODBC)

Cleanup typos (like SKIPP -> SKIP)

Extended MODIFY and CHANGE in ALTER TABLE to accept the AFTER keyword.
Extended MyISAM to handle records > 16M.

Fixes for embedded server
Made key_cache more configurable
Fixed that one can change key blocksize in MyISAM
A lot of optimizations to make MyISAM slightly faster

Fix problem with MyISAM and rows of length 65517-65520

Fixed that @VAR shows all decimals
Fixed problem with FLUSH TABLES and LOCK TABLE
CREATE ... SELECT now creates keys later
Reset AUTO_INCREMENT order if droping AUTO_INCREMENT key

Changed errmsg -> my_errmsg (portability issue)
Fixed that mysqlbinlog writes SET TIMESTAMP before all queries
Fixed comments in default my.cnf files