Fix documentation copy-paste bugs.
Fix documentation copy-paste bugs.

Fixes #5450.

Also improve the documentation of fromListWith.

Zigazou/containers,shockkolate/containers,ekmett/containers,shockkolate/containers,iu-parfunc/containers,hvr/containers,hvr/containers,hvr/containers,Zigazou/containers,ekmett/containers,ekmett/containers,iu-parfunc/containers,iu-parfunc/containers,Zigazou/containers,meiersi/psqueues-old,shockkolate/containers