Remove not used flag CLIENT_CHANGE_USER

Don't use DBUG library for struct st_my_thread_var to make code less complicated.

into mysql.sashanet.com:/reiser-data/mysql-4.0

DBUG_ macro cleanup
buffer boundary cleanup
This changeset, although not fully tested, works for me better than 
anything I've had so far, including what is in the repository. I will 
push it unless something crashes while I am writing this :-)

into mysql.sashanet.com:/reiser-data/mysql-4.0

If no problems are discovered in the next week, this will make the replication
code ready for 4.0.2 release.

into teton.kitebird.com:/home/paul/mysql-4.0

into sinisa.nasamreza.org:/mnt/hdc/Sinisa/mysql-4.0

manual.texi	Make a few -ized -> -ised changes.

manual.texi	- Clean up DES function descriptions.
manual.texi	- Correct incorrect INET_NTOA() description.
manual.texi	- Break too-long lines in a few query examples.

manual.texi	Fix a too-long-line in query example.

into sinisa.nasamreza.org:/mnt/hdc/Sinisa/mysql-4.0