Add strlcpy helper

Same as kernel provides, adopted from Linux sources.

strlcpy is similar to strncpy but _always_ adds \0
at the end of string even if destination is shorter.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>