partially revert the before patches :(

this seems to be needed for multi-instance and slow modules. i'm not sure i understand
why this helps and really don't like this code here, but avoids some segfaults for now.

steps to reproduce were:
- dr mode, do 3-4 heavy instances of denoise (profiled), best with parametric blending
- delete one
- go back to lr mode.
usermanual: some fixes
defringe tuning: apply strength differently and tune some internal parameters
defringe tuning: correct wrong *2.0 in local average and have a minmax of 0.1f  + allow more strength
defringe tuning: apply strength exponentially instead
defringe tuning: correct out of bounds check in fib_latt (just for safety, should never really happen at runtime)