The problem is that in a MyISAM table the following column
after a varchar field gets corrupted, if varchar field is
extended.

This should be made to work without a copy in the future, but
I'm not sure if this code is ready yet. This fix will force copy
in this case. It will not do any harm to have it here, only makes
alter table a bit slower in this case. If this should work for
MyISAM, then the bug is somewhere else in that code.

Until it works, I propose this as a temporary fix or a workaround.
Test case for the bug has been added.

into  mysql.com:/home/alexi/innodb/mysql-5.1-ss547
 Null merge

into  mysql.com:/home/alexi/innodb/mysql-5.0-ss547-work
 Null merge

 Fix BUG#19542 "InnoDB doesn't increase the Handler_read_prev counter".

 Fix BUG#19542 "InnoDB doesn't increase the Handler_read_prev counter.
 

into  mysql.com:/home/psergey/mysql-5.1-merge2

into  xiphis.org:/home/acurtis/mysql-5.1-merge

into  mysql.com:/home/ndbdev/ngrishakin/mysql-5.1-new

  Delete: mysql-test/r/ndb_partition_range.result
.del-ndb_partition_list.result~7af68cd45e74abf:
  Delete: mysql-test/r/ndb_partition_list.result
.del-ndb_partition_key.result~68b9a59cff8c9840:
  Delete: mysql-test/r/ndb_partition_key.result
.del-ndb_partition_error.result~944f84894e323e9:
  Delete: mysql-test/r/ndb_partition_error.result
.del-ndb_blob_partition.result~fda88ddfc5477a7e:
  Delete: mysql-test/r/ndb_blob_partition.result
.del-ndb_partition_range.test~af8f9016b6648239:
  Delete: mysql-test/t/ndb_partition_range.test
.del-ndb_partition_list.test~940289b3d58595ca:
  Delete: mysql-test/t/ndb_partition_list.test
.del-ndb_partition_key.test~ed7b15c91f66558d:
  Delete: mysql-test/t/ndb_partition_key.test
.del-ndb_partition_error.test~2da477be29be041f:
  Delete: mysql-test/t/ndb_partition_error.test
.del-ndb_blob_partition.test~ea99ef9759705ce3:
  Delete: mysql-test/t/ndb_blob_partition.test

into  c-870ae253.1238-1-64736c10.cust.bredbandsbolaget.se:/home/pappa/bug19010

into  c-870ae253.1238-1-64736c10.cust.bredbandsbolaget.se:/home/pappa/bug19010

into  c-870ae253.1238-1-64736c10.cust.bredbandsbolaget.se:/home/pappa/bug19010

into  c-870ae253.1238-1-64736c10.cust.bredbandsbolaget.se:/home/pappa/bug19010

into  c-870ae253.1238-1-64736c10.cust.bredbandsbolaget.se:/home/pappa/bug19010

into  c-870ae253.1238-1-64736c10.cust.bredbandsbolaget.se:/home/pappa/bug19010

into  mysql.com:/home/ndbdev/jmiller/clones/mysql-5.1-new

  Updated per lars
rpl_row_flsh_tbls.test:
  updated per lars

into  neptunus.(none):/home/msvensson/mysql/mysql-5.1

into  mysql.com:/usr_rh9/home/elkin.rh9/MySQL/FIXES/5.1-bug19728_regex_win

regex is fixed for windows.

into  neptunus.(none):/home/msvensson/mysql/mysql-5.1

into  neptunus.(none):/home/msvensson/mysql/mysql-5.1

into  mysql.com:/home/mysql-5.1-19509.19509

into  mysql.com:/home/ndbdev/jmiller/clones/mysql-5.1-new

into  mysql.com:/home/mysql-5.1-19509

into  linux.site:/home/reggie/work/mysql-5.1-test

into  mysql.com:/home/psergey/mysql-5.1-merge6

into  mysql.com:/home/psergey/mysql-5.1-merge6

into  big_geek.:C:/Work/mysql/mysql-5.1-test

into  siva.hindu.god:/usr/home/tim/m/51/a.bug6061

into  mysql.com:/home/psergey/mysql-5.1-merge6

into  mysql.com:/home/psergey/mysql-5.1-merge6