1. Fix ddl_i18n_koi8r, ddl_i18n_utf8: explicitly specify character-sets
directory for mysqldump;
2. Fix crash in mysqldump if collation is not found;
3. Use proper way to compare character set names.


client/mysqldump.c:
  Prevent crash if collation does not exist.
mysql-test/t/ddl_i18n_koi8r.test:
  Explicitly specify character-sets-directory for mysqldump.
mysql-test/t/ddl_i18n_utf8.test:
  Explicitly specify character-sets-directory for mysqldump.
sql/sql_lex.cc:
  Use my_charset_same() function to check if the charset names are equal.