Rework parser expression rules
  Rework handling for "||" concat/or
  Eliminate some shift/reduce conflicts
  Add support for "xxx IS [ NOT ] truth_value"


mysql-test/r/ansi.result:
  Fix test for new BROKEN_NOT mode bit
mysql-test/r/bool.result:
  WL#638
    New test for BROKEN_NOT mode
    New test for "expr IS [NOT] truth_value" syntax
mysql-test/r/sql_mode.result:
  Fix test for new BROKEN_NOT mode bit
mysql-test/t/bool.test:
  WL#638
    New test for BROKEN_NOT mode
    New test for "expr IS [NOT] truth_value" syntax
sql/lex.h:
  WL#638
    "&&" and "AND" return different tokens,
    NOT token changed to NOT_SYM
    OR_OR_CONCAT token changed to OR_OR_SYM
    New token "UNKNOWN"
sql/mysql_priv.h:
  WL#638
    New mode: BROKEN_NOT
sql/mysqld.cc:
  WL#638
    New mode: BROKEN_NOT
sql/set_var.cc:
  WL#638
    New mode: BROKEN_NOT
    BROKEN_NOT is set in MYSQL323 and MYSQL40 modes
sql/sql_lex.cc:
  Bug#638
    Alter tokens returned by lexer depending upon sql_mode:
    Return NOT2_SYM token instead of NOT_SYM when in BROKEN_NOT mode
    Return OR2_SYM token instead of OR_OR_SYM when not in PIPES_AS_CONCAT mode
sql/sql_yacc.yy:
  WL#638
    Change grammar to respect proper SQL syntax for NOT
    Clean up grammar, eliminate >100 shift/reduce conflicts
    New support for "expr IS [NOT] truth_value" SQL syntax
    Remove or_or_concat() support func. New support func is_truth_value()