Add failing unserialize integer overflow test

[deeky666]

This is a weird bug I encountered. When having a script that contains an integer overflow, unserializing BloomFilter objects errors:

PHP 5

Notice: unserialize(): Error at offset 24 of 195 bytes

PHP 7

php: symbol lookup error: modules/bloomy.so: undefined symbol: smart_str_appendl

See attached test case.

Maybe this is related to #6

[deeky666]

Okay boiled it down to this line. If I remove the errno == ERANGE check, everything works fine. As my PHP src knowledge is rather limited, I am not sure whether this is the correct solution. Any ideas?