SERVER-12461 Use larger values to test for too large $position arguments.

The previous values were integers that were just 3 away from the largest
possible 64-bit integer, were parsed as the same float as the largest possible
integer, and so were accepted.  This changes them to be much much larger.

Signed-off-by: Benety Goh <benety@mongodb.com>
Merge remote-tracking branch 'upstream/master'