regarded as unsigned longlongss, not as floats. This make these values work
similar to values between 10000000000000000000 and 18446744073709551615.


mysql-test/r/bigint.result:
  Fixed results for bigints
mysql-test/t/bigint.test:
  Fixed results for bigints
sql/item.h:
  Mark unsigned big ints as unsigned
sql/sql_lex.cc:
  Returns numbers between 9223372036854775807 and 9999999999999999999 as unsigned 64 bit numbers