Most calls to strconv.ParseInt(x, 10, 0) should really be
calls to strconv.ParseInt(x, 10, 64) in order to ensure that they
do not overflow on 32b architectures.

Furthermore, we should document a bug where Uid and Gid may
overflow on 32b machines since the type is declared as int.

Change-Id: I99c0670b3c2922e4a9806822d9ad37e1a364b2b8
Reviewed-on: https://go-review.googlesource.com/28472
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>