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‘model.frame()’ (used by ‘lm()’ and many other modelling functions) now
warns when it drops contrasts from factors. (Wish of PR#16119)
Port Tomas Kalibera's fix from R-devel that restores the loadMethod fast path, effectively doubling the speed of S4 dispatch.
If a package was updated and attached when its namespace was already loaded, it could end up with parts from one version and parts from the other. (PR#16120)