Implement mysql_change_user
Get rid of double user search at authentication
Some cleanups

Commit for merge 

into serg.mysql.com:/usr/home/serg/Abk/mysql-4.1

moved SQLCOM_END to the end of the list
bad copy-paste in sql_yacc.yy fixed

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

into bar.mysql.r18.ru:/usr/home/bar/mysql-4.1.wrk

fixed naming bug
fixed bug of subselect excluding

  renamed arg name to avoid a warning that it shadows global variable

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

after merge fix

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

into myvenu.com:/home/venu/bk/src-4.1

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

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

fixed sunction-test select in IN bug
fixed unions in subselect bug

sql_yacc.yy and sql_parse.cc cleanup

  libmysys.a is needed for my_errno

into mysql.r18.ru:/usr/home/ram/mysql-4.1