bugfix: incorrect pipeline depth and read addressing for increments.

Lesson learnt: testing with multiple identical threads will ease
debugging of gross errors, but hides misalignment errors: a thread
will get the correct value from *another* thread.

Fmax: 464/495/516 (phew!)
Simple pseudo-stencil hailstone testbench works!

Uses two post-incr. pointers, and multi-way branching!
All paths (even, odd, init) take 4 cycles
Average of 4.55 cycles over 10 generated results.