Bugfix, collating large numbers, greater than 2^53, skips -1 precision.

[prataprc]

While collating large uint64 and int64 that are outside the bounds of floating point precision for integers, we are self composing a e-notation for such numbers. While doing so, we are supposed to use -1 precision https://golang.org/pkg/strconv/#FormatFloat.

Solution: Use math/big in such cases.