Use more compact representation for packed arrays.

- for packed arrays we store just an array of zvals without keys.
- the elements of packed array are accessible throuf as ht->arPacked[i]
  instead of ht->arData[i]
- in addition to general ZEND_HASH_FOREACH_* macros, we introduced similar
  familied for packed (ZEND_HASH_PACKED_FORECH_*) and real hashes
  (ZEND_HASH_MAP_FOREACH_*)
- introduced an additional family of macros to access elements of array
  (packed or real hashes) ZEND_ARRAY_ELEMET_SIZE, ZEND_ARRAY_ELEMET_EX,
  ZEND_ARRAY_ELEMET, ZEND_ARRAY_NEXT_ELEMENT, ZEND_ARRAY_PREV_ELEMENT
- zend_hash_minmax() prototype was changed to compare only values

Because of smaller data set, this patch may show performance improvement
on some apps and benchmarks that use packed arrays. (~1% on PHP-Parser)

TODO:
    - sapi/phpdbg needs special support for packed arrays (WATCH_ON_BUCKET).
    - zend_hash_sort_ex() may require converting packed arrays to hash.

sapi/cli/php_cli_server.c

@@ -398,7 +398,7 @@ PHP_FUNCTION(apache_request_headers) /* {{{ */
 
 	array_init_size(return_value, zend_hash_num_elements(headers));
 
-	ZEND_HASH_FOREACH_STR_KEY_PTR(headers, key, value) {
+	ZEND_HASH_MAP_FOREACH_STR_KEY_PTR(headers, key, value) {
 		ZVAL_STRING(&tmp, value);
 		zend_symtable_update(Z_ARRVAL_P(return_value), key, &tmp);
 	} ZEND_HASH_FOREACH_END();