is_serialized() doesn't account for objects using PHP Serializable interface

[nerrad]

About Serializable -> ​http://us2.php.net/serializable

The problem: Serializable uses the token "C" at the beginning of the serialized string. This doesn't get recognized by Is_serialized() as a serialized string and thus doesn't get unserialized when maybe_unserialize is used.

The fix: Add the "C" token to the switch check in is_serialized().

See attached patch

[nerrad]

fix for is_serialized() to use "C" token

[dd32]

Duplicate of #17375.