Description:
------------
1. comparing to the 'stdClass' class name is done incorrectly. the word 'stdclass' instead of 'stdClass' is used.

2. Serializer doesn't not support the externalizable classes (AMF3 Specs).

I made a patch fixing the problems, described above

Reproduce code:
---------------
Index: amfext/amf.c
===================================================================
RCS file: /repository/pecl/amfext/amf.c,v
retrieving revision 1.4
diff -u -p -r1.4 amf.c
--- amfext/amf.c	23 Jul 2008 20:23:03 -0000	1.4
+++ amfext/amf.c	12 Aug 2008 09:15:10 -0000
@@ -100,7 +100,7 @@ enum AMF0Codes { AMF0_NUMBER, AMF0_BOOLE
 enum AMF3Codes { AMF3_UNDEFINED,AMF3_NULL,AMF3_FALSE,AMF3_TRUE,AMF3_INTEGER,AMF3_NUMBER,AMF3_STRING,AMF3_XML, AMF3_DATE, AMF3_ARRAY,AMF3_OBJECT, AMF3_XMLSTRING,AMF3_BYTEARRAY};
 
 /**  return values for callbacks */
-enum AMFCallbackResult { AMFC_RAW, AMFC_XML, AMFC_OBJECT, AMFC_TYPEDOBJECT, AMFC_ANY, AMFC_ARRAY,AMFC_NONE,AMFC_BYTEARRAY};
+enum AMFCallbackResult { AMFC_RAW, AMFC_XML, AMFC_OBJECT, AMFC_TYPEDOBJECT, AMFC_ANY, AMFC_ARRAY,AMFC_NONE,AMFC_BYTEARRAY, AMFC_EXTERNAL};
 
 /**  flags passed to amf_encode and amf_decode */
 enum AMFFlags { AMF_AMF3 = 1, AMF_BIGENDIAN=2,AMF_ASSOC=4,AMF_POST_DECODE = 8,AMF_AS_STRING_BUILDER = 16, AMF_TRANSLATE_CHARSET = 32,AMF_TRANSLATE_CHARSET_FAST = 32|64};
@@ -1178,7 +1178,7 @@ static void amf3_serialize_object(amf_se
 		return;
 	}
 
-	if(strcmp(className, "stdclass") == 0)  /*  never for resource */
+	if(strcmp(className, "stdClass") == 0)  /*  never for resource */
 		amf3_serialize_object_default(buf, Z_OBJPROP_PP(struc), "",0,var_hash TSRMLS_CC);
 	else
 	{
@@ -1278,7 +1278,16 @@ static void amf3_serialize_object(amf_se
 				php_error_docref(NULL TSRMLS_CC, E_NOTICE, "amf encoding callback. AMFC_TYPEDOBJECT requires an object or an array");
 			}
 			break;
-		case AMFC_ANY: amf3_serialize_var(buf, resultValue, var_hash TSRMLS_CC); break;
+		case AMFC_ANY: 
+			amf3_serialize_var(buf, resultValue, var_hash TSRMLS_CC); break;
+
+		case AMFC_EXTERNAL:
+			// all three lower bits have to be 1
+			amf3_write_objecthead(buf, 7 AMFTSRMLS_CC);
+			amf3_write_string(buf, className,classNameLen,AMF_STRING_AS_TEXT,var_hash TSRMLS_CC);
+			amf3_serialize_var(buf, resultValue, var_hash TSRMLS_CC);
+			break;
+
 		case AMFC_NONE: amf_write_byte(buf,AMF3_UNDEFINED); break;
 		case AMFC_BYTEARRAY:
 			if(Z_TYPE_PP(resultValue) == IS_STRING)
@@ -1387,7 +1396,7 @@ static void amf0_serialize_object(amf_se
 		return;
 	}
 
-	if(strcmp(className, "stdclass") == 0)
+	if(strcmp(className, "stdClass") == 0)
 	{
 		amf_write_byte(buf,AMF0_OBJECT);
 		amf0_serialize_objectdata(buf, Z_OBJPROP_PP(struc), 0, var_hash TSRMLS_CC);