crc32, md5 & sha1 functions

crc32, md5 and sha1 functions, implemented in PHP, are widely used for computing "fingerprint" of any data. But current implementation has not very good limitation - there is no way to get/set current state vector of these functions. So, we have to pass whole amount of data as argument of these functions at once instead of sequently data processing. Of course, we can use md5_file() or sha1_file() to get hash of huge amounts of data, but there is missing crc32_file() analog. I think, the best way is to add optional parameter to these functions, which will allow to get/set current state vector of hash algorithms. This change will not break backward compatibility.