This patch expands the docstring of `cl-reduce` to mention that the 
order of arguments to the given lambda is flipped when `:from-end` is 
used. This behaviour matches "right folds" in other languages, but this 
fact is otherwise hidden until the user's code suddenly breaks. The 
order flip is technically mentioned in the cl-lib manual, but in a 
somewhat cryptic way.

Cheers,

Colin