update mercurial to 3.7.1 in rawhide and F24

[Neal Becker]

I'd like to update to latest mercurial.  I built 3.7.1 in rawhide, and 
AFAICT there's no problem using it with tortoisehg-3.7.1-fc24.

I'd like to update mercurial in F24 - AFAIK there should not be any
compatibility issues.

Any objections?