Support utf16/utf32 charset and utf16_bin/utf32_bin collation in MySQL

[Jun Omae]

In Trac 1.0.10 with MySQL utf16/utf32, initenv command crashes:

Database connection string [sqlite:db/trac.db]> mysql://tracuser:password@127.0.0.1/trac_utf16

Creating and Initializing Project
Initenv for '/dev/shm/trac-1.0.10-mysql-utf16' failed.
Failed to create environment.
(1231, "Variable 'character_set_client' can't be set to the value of 'utf16'")
Traceback (most recent call last):
  File "/venv/trac/1.0.10/lib/python2.5/site-packages/trac/admin/console.py", line 461, in do_initenv
    options=options)
  File "/venv/trac/1.0.10/lib/python2.5/site-packages/trac/core.py", line 124, in __call__
    self.__init__(*args, **kwargs)
  File "/venv/trac/1.0.10/lib/python2.5/site-packages/trac/env.py", line 280, in __init__
    self.create(options)
  File "/venv/trac/1.0.10/lib/python2.5/site-packages/trac/env.py", line 602, in create
    DatabaseManager(self).init_db()
  File "/venv/trac/1.0.10/lib/python2.5/site-packages/trac/db/api.py", line 253, in init_db
    connector.init_db(**args)
  File "/venv/trac/1.0.10/lib/python2.5/site-packages/trac/db/mysql_backend.py", line 117, in init_db
    params)
  File "/venv/trac/1.0.10/lib/python2.5/site-packages/trac/db/mysql_backend.py", line 98, in get_connection
    cnx = MySQLConnection(path, log, user, password, host, port, params)
  File "/venv/trac/1.0.10/lib/python2.5/site-packages/trac/db/mysql_backend.py", line 374, in __init__
    cnx.query("SET NAMES %s" % self.charset)
OperationalError: (1231, "Variable 'character_set_client' can't be set to the value of 'utf16'")

If supplementary characters is needed, we have to use utf8mb4 charset. However, max size of column would be short because 1 character requires 4 bytes for index. Since MySQL 5.5.3, utf16 supports supplementary characters using surrogate pair. 1 character in utf16 requires 2 bytes for index.