Fix more int overflow issues in hashtable
Fix more int overflow issues in hashtable

Previous commit fixes the main hash addressing, this adds further
repairs to hash expansion and hash table walker.

HASHPOWER_MAX stays at 32, since the computed hashvalue is 32bit and
going beyond that would break things rather badly :)

memcached/memcached,memcached/memcached,dormando/memcached,memcached/memcached,dormando/memcached,dormando/memcached,memcached/memcached,dormando/memcached,dormando/memcached,memcached/memcached