Problem:
    mysqld --collation-server=xxx --character-set-server=yyy
    didn't work as expected: collation_server was set not to xxx,
    but to the default collation of character set "yyy".
    
    With different argument order it worked as expected:
    mysqld --character-set-server=yyy --collation-server=yyy 
    
    Fix:
    initializate default_collation_name to 0
    when processing --character-set-server
    only if --collation-server has not been specified
    in command line.



mysql-test/r/ctype_ucs2_def.result:
  Adding test case
mysql-test/t/ctype_ucs2_def-master.opt:
  Specifying variables in reverse order, to cover the bug.
mysql-test/t/ctype_ucs2_def.test:
  Adding test case
sql/mysqld.cc:
  Don't clear default_collation_name when processing 
      --character-set-server if collation has already
      been specified using --collation-server