Remember data (allocation) size of non-extension data from headerGet()

- Add size member to rpmtd_s and accessor function to get it.
  For now only works for data marked with RPMTD_IMMUTABLE.
- This is redundant for BIN type, but especially for string types this
  info is impossible to get without walking the entire data.

lib/header.c

@@ -1176,6 +1176,7 @@ static int copyTdEntry(const indexEntry entry, rpmtd td, headerGetFlags flags)
     }
     td->type = entry->info.type;
     td->count = count;
+    td->size = entry->length;
 
     if (td->data && entry->data != td->data) {
 	td->flags |= RPMTD_ALLOCED;

lib/rpmtd.c

@@ -57,6 +57,11 @@ rpm_count_t rpmtdCount(rpmtd td)
     return (td->type == RPM_BIN_TYPE) ? 1 : td->count;
 }
 
+rpm_count_t rpmtdSize(rpmtd td)
+{
+    return (td != NULL) ? td->size : 0;
+}
+
 rpmTagVal rpmtdTag(rpmtd td)
 {
     assert(td != NULL);

lib/rpmtd.h

@@ -30,6 +30,7 @@ struct rpmtd_s {
     rpm_data_t data;	/* pointer to actual data */
     rpmtdFlags flags;	/* flags on memory allocation etc */
     int ix;		/* iteration index */
+    rpm_count_t size;	/* size of data (only works for RPMTD_IMMUTABLE atm) */
 };
 
 /** \ingroup rpmtd
@@ -66,6 +67,14 @@ void rpmtdFreeData(rpmtd td);
  */
 rpm_count_t rpmtdCount(rpmtd td);
 
+/** \ingroup rpmtd
+ * Retrieve container data size (eg required for allocation).
+ * Note this currently only works for RPMTD_IMMUTABLE data.
+ * @param td		Tag data container
+ * @return		Data size in bytes.
+ */
+rpm_count_t rpmtdSize(rpmtd td);
+
 /** \ingroup rpmtd
  * Retrieve tag of the container.
  * @param td		Tag data container