add API for fingerprints function with callback data.

This change is backwards compatible.  It adds two new functions, is_sqli2() and is_string_sqli2() which take a ptr_fingerprints2_fn instead of a ptr_fingerprint_fn and an extra void* callback data argument.  ptr_fingerprints2_fn is int (*)(const char*, void*) and the callback data passed to is_sqli() is then forwarded to the fingerprints function.