support callback data for fingerprints function.

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.

This functionality is needed in IronBee to support user defined fingerprint sets.  I.e., the callback data will be used to pass in an datastructure to look the fingerprint up in.