Cherry pick missing LoKi functor fix to 2018-patches

Mark Smithrequested to merge
cherry-pick-6e5834f3 into 2018-patches

Completely Trivial: Add two new functor 'shortcuts' for MCMAXTREE and MCMINTREE

See merge request !3537 (merged)

(cherry picked from commit 6e5834f3)

a9b2fd7e Add two new functor 'shortcuts' for MCMAXTREE and MCMINTREE

Edited by Mark Smith

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