bit64 should be auto loaded with rkdb

[lwshang]

R package bit64 provide support for 64 bit integer which is used in current version of rkdb. However, it is not auto loaded when we library(rkdb). It will be loaded when an execute call involve q timestamp because nanotime is loaded then.

This behavior can cause some problem.

> library(rkdb)
> h <- open_connection()
> execute(h, "1")
[1] 0
attr(,"class")
[1] "integer64"

The q long integer 1 was not transformed to R correctly.

We can explicitly load bit64.

> library(bit64)
> execute(h, "1")
integer64
[1] 1