Safely invoke scope expiration functions within try...finally form.
Removed rpc parameters from debug output.

Parameters may contain big amounts of data and hence clutter up the output.
Fixed a major performance bottleneck in payload-masking function.

A first ca. 10 times improvement was gained by converting the arguments
passed to "bit-xor" to ints: (bit-xor (int a) (int b)).

A second ca. 6 times improvement was achieved by directly accessing the
mask bytes array using aget.