SHA-3 Keccak_Hash: Store Keccak_HashInstance in the main context.

SHA-3 Keccak_Hash: Store Keccak_HashInstance in the main context.

Previously, the Keccak_HashInstance was separately allocated.
This could cause memory leaks on errors. For instance,
in php_hash_do_hash_hmac, the following code cleans up after
a file read error:

    if (n < 0) {
    	efree(context);
    	efree(K);
    	zend_string_release(digest);
    	RETURN_FALSE;
    }

This does not call the context's hash_final operation, which
was the only way to free the separately-allocated Keccak state.

The simplest fix is simply to place the Keccak_HashInstance state
inside the context object. Then it doesn't need to be freed.

As a result, there is no need to call hash_final in the
HashContext destructor: HashContexts cannot contain internally
allocated resources.