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


client/mysqladmin.c:
  Fix long line
include/mysql_com.h:
  Fix long lines
libmysql/libmysql.c:
  mysql_change_user() for new auth + some fixes
sql/password.c:
  Add author info so who is guilty in errors would be known :)
sql/sql_acl.cc:
  Move class definitions to .h
sql/sql_acl.h:
  Add class definitions
sql/sql_parse.cc:
  Get rid of double user search. Implement mysql_change_user