mode".

Changed grammar rule for "type" token. Now we have one branch with 
optional length specification for TIMESTAMP type instead of two separate
branches.


mysql-test/r/type_timestamp.result:
  Added test case for bug #7418 "TIMESTAMP not always converted to DATETIME
  in MAXDB mode".
mysql-test/t/type_timestamp.test:
  Added test case for bug #7418 "TIMESTAMP not always converted to DATETIME
  in MAXDB mode".
sql/sql_yacc.yy:
  Changed rule for "type" token. Now we have one branch with optional
  length specification for TIMESTAMP type instead of two separate branches.
  This also gives us consistent behavior for TIMETSAMP in MAXDB mode.