Change the default internal weight to 1 from 0

If the default internal weight is 0, "weight 10" produces "score
11". It is strange.

The following chunks in ii.c may be wrong:

    @@ -5705,7 +5705,7 @@ grn_ii_similar_search(grn_ctx *ctx, grn_ii *ii,
             while (grn_ii_cursor_next(ctx, c)) {
               pos = c->post;
               if ((w2 = get_weight(ctx, s, pos->rid, pos->sid, wvm, optarg))) {
    -            res_add(ctx, s, (grn_rset_posinfo *) pos, *w1 * w2 * (pos->tf + pos->weight), op);
    +            res_add(ctx, s, (grn_rset_posinfo *) pos, *w1 * w2 * pos->tf * pos->weight, op);
               }
             }
           }

    @@ -5926,6 +5926,7 @@ grn_ii_select(grn_ctx *ctx, grn_ii *ii, const char *string, unsigned int string_
                   if (max - min <= max_interval) {
                     if (rep) { pi.pos = min; res_add(ctx, s, &pi, weight, op); }
                     noccur++;
    +                tscore += ti->p->weight; /* FIXME: Is it right? */
                     if (ti->pos == max + 1) {
                       break;
                     }

    @@ -5950,14 +5951,14 @@ grn_ii_select(grn_ctx *ctx, grn_ii *ii, const char *string, unsigned int string_
    ...
    -              tscore += score;
    +              tscore += score / count;
                   score = 0; count = 0; pos++;
                   noccur++;
    ...

    @@ -5950,14 +5951,14 @@ grn_ii_select(grn_ctx *ctx, grn_ii *ii, const char *string, unsigned int string_
    ...
                 }
               }
             }
    -        if (noccur && !rep) { res_add(ctx, s, &pi, (noccur + tscore) * weight, op); }
    +        if (noccur && !rep) { res_add(ctx, s, &pi, (noccur * tscore) * weight, op); }