Fix for BUG#13897 "failure to do SET SQL_MODE=N where N is a number > 31" (the original bug's title isn't the simplest
symptom). sys_var::check_set() was wrong. mysqlbinlog makes use of such SET SQL_MODE=N
(where N is interpreted like if SQL_MODE was a field of type SET), so
this bug affected recovery from binlogs if the server was running with certain SQL_MODE values,
for example the default values on Windows (STRICT_TRANS_TABLES); to work around this bug people
had to edit mysqlbinlog's output.


mysql-test/r/sql_mode.result:
  result update
mysql-test/t/sql_mode.test:
  test for various numeric SQL_MODE values
sql/set_var.cc:
  For a set, it does not make sense to test if the supplied argument exceeds the number of elements in the set
  (such test would make sense for an enum), but rather to check if it exceeds 2^this (to verify
  that only reasonable bits are set).