Scanner and parser use different tables for constants

Moreover, each function being parsed has its own table.

The code is cleaner when each table is used for one specific purpose:
The scanner uses its table to anchor and unify strings, mapping strings
to themselves; the parser uses it to reuse constants in the code,
mapping constants to their indices in the constant table. A different
table for each task avoids false collisions.

lparser.c

@@ -737,6 +737,7 @@ static void codeclosure (LexState *ls, expdesc *v) {
 
 
 static void open_func (LexState *ls, FuncState *fs, BlockCnt *bl) {
+  lua_State *L = ls->L;
   Proto *f = fs->f;
   fs->prev = ls->fs;  /* linked list of funcstates */
   fs->ls = ls;
@@ -757,8 +758,11 @@ static void open_func (LexState *ls, FuncState *fs, BlockCnt *bl) {
   fs->firstlabel = ls->dyd->label.n;
   fs->bl = NULL;
   f->source = ls->source;
-  luaC_objbarrier(ls->L, f, f->source);
+  luaC_objbarrier(L, f, f->source);
   f->maxstacksize = 2;  /* registers 0/1 are always valid */
+  fs->kcache = luaH_new(L);  /* create table for function */
+  sethvalue2s(L, L->top.p, fs->kcache);  /* anchor it */
+  luaD_inctop(L);
   enterblock(fs, bl, 0);
 }
 
@@ -780,6 +784,7 @@ static void close_func (LexState *ls) {
   luaM_shrinkvector(L, f->locvars, f->sizelocvars, fs->ndebugvars, LocVar);
   luaM_shrinkvector(L, f->upvalues, f->sizeupvalues, fs->nups, Upvaldesc);
   ls->fs = fs->prev;
+  L->top.p--;  /* pop kcache table */
   luaC_checkGC(L);
 }