Merge pull request #2686 from cubicdaiya/use-suitable-type

Use suitable type.

src/string.c

@@ -1310,7 +1310,7 @@ mrb_str_index_m(mrb_state *mrb, mrb_value str)
 
   switch (mrb_type(sub)) {
     case MRB_TT_FIXNUM: {
-      int c = mrb_fixnum(sub);
+      mrb_int c = mrb_fixnum(sub);
       mrb_int len = RSTRING_LEN(str);
       unsigned char *p = (unsigned char*)RSTRING_PTR(str);
 
@@ -1656,7 +1656,7 @@ mrb_str_rindex_m(mrb_state *mrb, mrb_value str)
 
   switch (mrb_type(sub)) {
     case MRB_TT_FIXNUM: {
-      int c = mrb_fixnum(sub);
+      mrb_int c = mrb_fixnum(sub);
       unsigned char *p = (unsigned char*)RSTRING_PTR(str);
 
       for (pos=len-1;pos>=0;pos--) {