re: lua(4), non-invasive and invasive parts

[matthew green]

this is going to upset dyoung i'm sure :) but it seems to me that
if these invasive changes to individual subsystems are needed like
this, and we want them to be optional, then imo they should be on
a per-subsystem basis, not global.  eg something like:

        options LINEDISC_LUA
        options GPIOSIM_LUA

etc.  the ugliness could/should be largely hidden in header files.


.mrg.