R1:b9ba0418ed13

Correct a parameter order swap in "diffusion.historyquery" for Mercurial

Summary: Ref T13666. See T13666#256253. The order of these parameters is incorrect (introduced in D18817, which was trying to turn the revset "A or B" into "B or A"), but when "commit" is the single head of "branch" (which is common), the revset is functionally equivalent.

Test Plan:
An easy reproduction case is to make a "diffusion.historyquery" call manually against a Mercurial repository, with a valid "branch" name and some non…