tweak interface to do the right thing, after useful comments from millert@

(mostly use a calloc function to avoid potential integer overflow)

src/include/ohash.h

@@ -1,6 +1,6 @@
 #ifndef OHASH_H
 #define OHASH_H
-/* $OpenBSD: ohash.h,v 1.10 2012/09/23 15:05:23 espie Exp $ */
+/* $OpenBSD: ohash.h,v 1.11 2014/05/12 19:07:37 espie Exp $ */
 /* ex:ts=8 sw=4: 
  */
 
@@ -24,16 +24,18 @@
  * techniques, and more efficient in most cases.
  */
 
+/* user-visible data structure */
 struct ohash_info {
 	ptrdiff_t key_offset;
 	void *data;	/* user data */
-	void *(*halloc)(size_t, void *);
-	void (*hfree)(void *, size_t, void *);
+	void *(*calloc)(size_t, size_t, void *);
+	void (*free)(void *, void *);
 	void *(*alloc)(size_t, void *);
 };
 
 struct _ohash_record;
 
+/* private structure. It's there just so you can do a sizeof */
 struct ohash {
 	struct _ohash_record 	*t;
 	struct ohash_info 	info;