bug#13004: 24.2; vc-diff from vc-log doesn't show diff before renames (for Mercurial backend).

[Glenn Morris]

Oleksandr Gavenko wrote:

> **PS** Why Emacs uses -r R1 -r R2 for HG? "-c" - do job more better as it
>        actually compares to its first parent.

Because the Emacs command is a specific instance of the general question
"find the difference between revisions R1 and R2". Naively, I expect
these two to be exactly equivalent when R2 = R1 + 1. `bzr help diff'
says they are, I didn't check.