-------------------------------------------
variable: $mstrength -- strength normal img force in shrink()
-------------------------------------------
default: 0.125

This floating point parameter (F3 panel, lower
right) controls the strength of the normal image
force in shrink() and shrink_to_fill().

For the default forcemode (0), the normal image
force is calculated as:

  force = mstrength*tanh((val - mmid)*mslope);

See R-click help for $forcemode for more details.
