Cleaning of llimits.h

Several definitions that don't need to be "global" (that is, that
concerns only specific parts of the code) moved out of llimits.h,
to more appropriate places.

lobject.h

@@ -538,6 +538,9 @@ typedef struct Udata0 {
 #define LUA_VPROTO	makevariant(LUA_TPROTO, 0)
 
 
+typedef l_uint32 Instruction;
+
+
 /*
 ** Description of an upvalue for function prototypes
 */