Fix for unserialise() "vulnerabilities"

Hi, I've found, that at least half of unserialise() security problems, occurs because of non-symmetric serialize/unserialize assumption, regarding references encoded with "r". serialize() assumes it's an object. https://github.com/php/php-src/blob/master/ext/standard/var.c#L828 universalize() allows any value. https://github.com/php/php-src/blob/master/ext/standard/var_unserializer.re#L677 This allows manual crafting of strings that may lead to creation of unexpected data structures. I propose to fix this just by fixing the symmetry. https://gist.github.com/dstogov/53382540bdfee7b6c7dadf142dc437ed This will prohibit, some manually crafted strings. Of course, this will break few "security" related tests. Especially: > Bug #70284 (Use after free vulnerability in unserialize() with GMP) > [ext/gmp/tests/bug70284.phpt] > Bug #70211 (php 7 ZEND_HASH_IF_FULL_DO_RESIZE use after free) [ext/soap/tests/bug70211.phpt] > Bug #70172 - Use After Free Vulnerability in unserialize() > [ext/standard/tests/serialize/bug70172.phpt] > Bug #70963 (Unserialize shows UNKNOW in result) [ext/standard/tests/serialize/bug70963.phpt] > Memleaks if unserialize return a self-referenced array/object > [ext/standard/tests/serialize/unserialize_mem_leak.phpt] > Bug #72433: Use After Free Vulnerability in PHP's GC algorithm and unserialize > [ext/standard/tests/strings/bug72433.phpt] Any objections? (this is for master only of course) Thanks. Dmitry.