Add per-datatype iterators to rpmtd

- just uint32 and string iterators for now, those are the most common ones
- allows somewhat more convenient code constructs when type is known,
  eg no need to separately check for non-null inside loops

lib/rpmtd.c

@@ -96,6 +96,26 @@ int rpmtdNext(rpmtd td)
     return i;
 }
 
+uint32_t *rpmtdNextUint32(rpmtd td)
+{
+    assert(td != NULL);
+    uint32_t *res = NULL;
+    if (rpmtdNext(td) >= 0) {
+	res = rpmtdGetUint32(td);
+    }
+    return res;
+}
+
+const char *rpmtdNextString(rpmtd td)
+{
+    assert(td != NULL);
+    const char *res = NULL;
+    if (rpmtdNext(td) >= 0) {
+	res = rpmtdGetString(td);
+    }
+    return res;
+}
+
 char * rpmtdGetChar(rpmtd td)
 {
     char *res = NULL;

lib/rpmtd.h

@@ -86,6 +86,20 @@ int rpmtdInit(rpmtd td);
  */
 int rpmtdNext(rpmtd td);
 
+/** \ingroup rpmtd
+ * Iterate over uint32_t type tag data container.
+ * @param td		Tag data container
+ * @return		Pointer to next value, NULL on termination or error
+ */
+uint32_t *rpmtdNextUint32(rpmtd td);
+
+/** \ingroup rpmtd
+ * Iterate over string / string array type tag data container.
+ * @param td		Tag data container
+ * @return		Pointer to next value, NULL on termination or error
+ */
+const char *rpmtdNextString(rpmtd td);
+
 /** \ingroup rpmtd
  * Return char data from tag container.
  * For scalar return type, just return pointer to the integer. On array