do not look for client-specific commands while inside a multi-line comment.
we will allow multi-comments pretty much anywhere within SQL-statements,
but client-specific commands (help, use, print, ...) must be the first token
in the input.


client/mysql.cc:
  Bug#20432: mysql client interprets commands in comments
mysql-test/r/mysql_client.result:
  Bug#20432: mysql client interprets commands in comments
  test client-side parsing of comments and client-specific commands
mysql-test/t/mysql_client.test:
  Bug#20432: mysql client interprets commands in comments
  test client-side parsing of comments and client-specific commands