Rename API mrb_str_cat2() to mrb_str_cat_cstr(). This is for naming orthogonality. mrb_str_cat2() is also left for backward compatibility.

src/error.c

@@ -136,7 +136,7 @@ exc_inspect(mrb_state *mrb, mrb_value exc)
       mrb_str_append(mrb, str, mesg);
       mrb_str_cat(mrb, str, " (", 2);
     }
-    mrb_str_cat2(mrb, str, mrb_obj_classname(mrb, exc));
+    mrb_str_cat_cstr(mrb, str, mrb_obj_classname(mrb, exc));
     if (!mrb_nil_p(mesg) && RSTRING_LEN(mesg) > 0) {
       mrb_str_cat(mrb, str, ")", 1);
     }
@@ -148,7 +148,7 @@ exc_inspect(mrb_state *mrb, mrb_value exc)
       mrb_str_append(mrb, str, mesg);
     } else {
       mrb_str_cat(mrb, str, ": ", 2);
-      mrb_str_cat2(mrb, str, mrb_obj_classname(mrb, exc));
+      mrb_str_cat_cstr(mrb, str, mrb_obj_classname(mrb, exc));
     }
   }
   return str;

src/string.c

@@ -2548,7 +2548,7 @@ mrb_str_cat(mrb_state *mrb, mrb_value str, const char *ptr, mrb_int len)
 }
 
 mrb_value
-mrb_str_cat2(mrb_state *mrb, mrb_value str, const char *ptr)
+mrb_str_cat_cstr(mrb_state *mrb, mrb_value str, const char *ptr)
 {
   return mrb_str_cat(mrb, str, ptr, strlen(ptr));
 }