MFH: do not allow to implement the same interface twice

add tests

Zend/tests/objects_012.phpt

@@ -0,0 +1,15 @@
+--TEST--
+implementing a class
+--FILE--
+<?php
+
+class foo {
+}
+
+interface bar extends foo {
+}
+
+echo "Done\n";
+?>
+--EXPECTF--	
+Fatal error: bar cannot implement foo - it is not an interface in %s on line %d

Zend/tests/objects_013.phpt

@@ -0,0 +1,15 @@
+--TEST--
+implementing the same interface twice
+--FILE--
+<?php
+
+interface foo {
+}
+
+class bar implements foo, foo {
+}	
+
+echo "Done\n";
+?>
+--EXPECTF--	
+Fatal error: Cannot implement previously implemented interface foo in %s on line %d

Zend/tests/objects_014.phpt

@@ -0,0 +1,15 @@
+--TEST--
+extending the same interface twice
+--FILE--
+<?php
+
+interface foo {
+}
+
+interface bar extends foo, foo {
+}	
+
+echo "Done\n";
+?>
+--EXPECTF--	
+Fatal error: Cannot implement previously implemented interface foo in %s on line %d

Zend/zend_compile.c

@@ -2247,6 +2247,17 @@ static zend_bool do_inherit_constant_check(HashTable *child_constants_table, zva
 
 ZEND_API void zend_do_implement_interface(zend_class_entry *ce, zend_class_entry *iface TSRMLS_DC)
 {
+	zend_uint i, if_num = ce->num_interfaces, cnt = 0;
+
+	for (i = 0; i < if_num; i++) {
+		if (ce->interfaces[i] != NULL && ce->interfaces[i]->name_length == iface->name_length && !memcmp(ce->interfaces[i]->name, iface->name, iface->name_length)) {
+			cnt++;
+			if (cnt > 1) {
+				zend_error(E_COMPILE_ERROR, "Cannot implement previously implemented interface %s", iface->name);
+			}
+		}
+	}
+
 	zend_hash_merge_ex(&ce->constants_table, &iface->constants_table, (copy_ctor_func_t) zval_add_ref, sizeof(zval *), (merge_checker_func_t) do_inherit_constant_check, iface);
 	zend_hash_merge_ex(&ce->function_table, &iface->function_table, (copy_ctor_func_t) do_inherit_method, sizeof(zend_function), (merge_checker_func_t) do_inherit_method_check, ce);