Add getgroups.
Add getgroups.

ardje/luaposix,zevv/luaposix,snegovick/luaposix,jimmyharris/luaposix,luaposix/luaposix,ardje/luaposix,snegovick/luaposix,rrthomas/luaposix,rrthomas/luaposix,zevv/luaposix,jimmyharris/luaposix