Quote PKEY.


mysql-test/t/mysqldump.test:
  Test for BUG#13926: --order-by-primary fails if PKEY contains quote character
mysql-test/r/mysqldump.result:
  Test results for BUG#13926: --order-by-primary fails if PKEY contains quote character
client/mysqldump.c:
  Fix for BUG#13926: --order-by-primary fails if PKEY contains quote character.
  Quote PKEY.