updated bit32 library for Lua 5.1.4

[Sean Bolton <sean@...>]

Previously, I backported the Lua 5.2 bit32 library to work
with Lua 5.1.x.  I've just updated the backport to the most
recent 5.2.0-beta-rc1 version, so it now includes the new
bit32.extract and bit32.replace operations. You can find it
here:

  http://smbolton.com/lua/lbitlib-5.2.0-beta-rc1-backport3.c

Have fun,

-Sean