by binlogging some SET ONE_SHOT CHARACTER_SETetc,
which will be enough until we have it more compact and more complete in 5.0. With the present patch,
replication will work ok between 4.1.3 master and slaves, as long as:
- master and slave have the same GLOBAL.COLLATION_SERVER
- COLLATION_DATABASE and CHARACTER_SET_DATABASE are not used
- application does not use the fact that table is created with charset of the USEd db (BUG#2326).
all of which are not too hard to fulfill. 
ONE_SHOT is reserved for internal use of mysqlbinlog|mysql and works only for charsets,
so we give error if used for non-charset vars.
Fix for BUG#3875 "mysqlbinlog produces wrong ouput  if query uses
 variables containing quotes" and BUG#3943 "Queries with non-ASCII literals are not replicated
 properly after SET NAMES".
Detecting that master and slave have different global charsets or server ids.


mysql-test/r/rpl_server_id1.result:
  it's normal to not run as I have added a test to compare server ids of master and slave
  at startup and stop if equal (unless --replicate-same-server-id)
mysql-test/r/rpl_user_variables.result:
  result update (as we now print charset of user var).
mysql-test/r/user_var.result:
  result update
mysql-test/t/rpl_server_id1.test:
  no need to select as slave is not running
mysql-test/t/user_var.test:
  testing if the content of user vars is escaped when mysqlbinlog prints them,
  and if the name is backquoted.
sql/lex.h:
  new keyword ONE_SHOT
sql/log.cc:
  when writing to the binlog, before writing the actual statement, write some SET ONE_SHOT CHARACTER_SET_CLIENT etc
  for the slave to know the charset variables (which are important as they affect the inserted data).
sql/log_event.cc:
  print charset and collation of user var in mysqlbinlog and SHOW BINLOG EVENTS.
  escape the content of the var. Backquote its name.
  Will ask Bar to check that using my_charset_bin for escaping is ok.
sql/set_var.cc:
  understand SET CHARACTER_SET_CLIENT=10 (don't require a string, accept a number).
  Refuse changing of GLOBAL CHARACTER_SET_SERVER/COLLATION_SERVER if binlog or slave,
  as it will make the master or slave make wrong assumptions.
  A function to catch SET ONE_SHOT on non-charset variables (which is forbidden)
sql/set_var.h:
  no_support_one_shot to know if the var supports ONE_SHOT (only charset vars do, soon timezones).
  Accept int arg in SET CHARACTER_SET_etc
sql/slave.cc:
  when I/O slave thread starts, verify that master's and slave charsets match.
  And by the way verify that server ids are different.
  Don't fail if UNIX_TIMESTAMP() can't be done on master (very old master), that's
  not fatal.
sql/sql_class.cc:
  one_shot
sql/sql_class.h:
  one_shot
sql/sql_lex.h:
  one_shot
sql/sql_parse.cc:
  when SET ONE_SHOT is used, verify that it's only used for charset/collation vars;
  otherwise refuse.
sql/sql_yacc.yy:
  ONE_SHOT keyword in SET