The reverted commit 968ce9af598024ec71e9ffb2d15c3997a13ad754
is suspected (through the use of bisection) of causing network slowdowns.
Revert for now as we are close to release.
Previously, when the CSM restriction 'LOAD_CLIENT_MODS' was used a
client was still able to add CSM code to 'builtin' to bypass that
restriction, because 'builtin' is not yet verified.
Until server-sent CSM and verifying of 'builtin' are complete, make
'LOAD_CLIENT_MODS' disable the loading of builtin.
Clarify code comments and messages to distinguish between client-side
modding and client-side scripting. 'Scripting' includes 'builtin',
'modding' does not.
