MB-7879: wrap python integers into c_uint64

Using Python values as they are is not safe. We must explicitly
specify uint64_t in order to avoid problems with 32-bit platforms.

All unit tests passed (both 32-bit and 64-bit GNU/Linux).

Change-Id: Id3c9544908f2c02ac94fcdf62f222d75740f3c89
Reviewed-on: http://review.couchbase.org/26131
Reviewed-by: Bin Cui <bin.cui@gmail.com>
Tested-by: Aaron Miller <apage43@ninjawhale.com>
Reviewed-by: Aaron Miller <apage43@ninjawhale.com>