Keep correct type for immediate operands in comparisons

When calling metamethods for things like 'a < 3.0', which generates
the opcode OP_LTI, the C register tells that the operand was
converted to an integer, so that it can be corrected to float when
calling a metamethod.

This commit also includes some other stuff:
- file 'onelua.c' added to the project
- opcode OP_PREPVARARG renamed to OP_VARARGPREP
- comparison opcodes rewritten through macros

ltm.c

@@ -205,9 +205,13 @@ int luaT_callorderTM (lua_State *L, const TValue *p1, const TValue *p2,
 
 
 int luaT_callorderiTM (lua_State *L, const TValue *p1, int v2,
-                       int inv, TMS event) {
+                       int inv, int isfloat, TMS event) {
   TValue aux; const TValue *p2;
-  setivalue(&aux, v2);
+  if (isfloat) {
+    setfltvalue(&aux, cast_num(v2));
+  }
+  else
+    setivalue(&aux, v2);
   if (inv) {  /* arguments were exchanged? */
     p2 = p1; p1 = &aux;  /* correct them */
   }