int64 to decimal string conversion

[Cosmin Apreutesei <cosmin.apreutesei@...>]

Hi,

This post may sound stupid, but I haven't found/been able to produce a
decent int64 (read as 2 ints or 8 bytes or whatever) to string
conversion function made in Lua without bitops or integer
multiplication past 52bit. Any hints/links? Just want to provide it as
a fallback to installing a bignum library in fbclient.

Thanks,
Cosmin.