PSYNC2: just store script bodies into RDB.

Related to #4483. As suggested by @soloestoy, we can retrieve the SHA1
from the body. Given that in the new implementation using AUX fields we
ended copying around a lot to create new objects and strings, extremize
such concept and trade CPU for space inside the RDB file.

src/scripting.c

@@ -1147,11 +1147,26 @@ int redis_math_randomseed (lua_State *L) {
  *
  *   f_<hex sha1 sum>
  *
+ * If 'funcname' is NULL, the function name is created by the function
+ * on the fly doing the SHA1 of the body, this means that passing the funcname
+ * is just an optimization in case it's already at hand.
+ *
+ * The function increments the reference count of the 'body' object as a
+ * side effect of a successful call.
+ *
  * On success C_OK is returned, and nothing is left on the Lua stack.
  * On error C_ERR is returned and an appropriate error is set in the
  * client context. */
 int luaCreateFunction(client *c, lua_State *lua, char *funcname, robj *body) {
     sds funcdef = sdsempty();
+    char fname[42];
+
+    if (funcname == NULL) {
+        fname[0] = 'f';
+        fname[1] = '_';
+        sha1hex(fname+2,body->ptr,sdslen(body->ptr));
+        funcname = fname;
+    }
 
     funcdef = sdscat(funcdef,"function ");
     funcdef = sdscatlen(funcdef,funcname,42);