lualoader: Actually re-raise error in try_include

It was previously only printed, but we do actually want to raise it as a
full blown error so that things don't look OK when they've actually gone
wrong.

The second parameter to error, level, is set to 2 here so that the error
message reflects the position of the try_include caller, rather than the
try_include itself. Example:

LUA ERROR: /boot/lua/loader.lua:46: /boot/lua/local.lua:1: attempt to call a
nil value (global 'cxcint').

stand/lua/core.lua

@@ -56,7 +56,7 @@ function try_include(module)
 	-- configuration will not display 'module not found'. All other errors
 	-- in loading will be printed.
 	if config.verbose or ret:match("^module .+ not found") == nil then
-		print(ret)
+		error(ret, 2)
 	end
 	return nil
 end