failure emails assume nixpkgs changes are to blame

[Glenn Morris]

Hi,

A minor issue:

When a job switches from success to failure, eg

http://lists.gnu.org/archive/html/emacs-buildstatus/2013-11/msg00000.html
http://lists.gnu.org/archive/html/emacs-buildstatus/2013-11/msg00011.html

there's a footer that says "This is likely due to N commits by X".

Based on the input changes in the first example:
http://hydra.nixos.org/build/6758185

it seems that it is referring to nixpkgs changes.
I guess these are unlikely to be the cause of most failures,
rather it is the changes in the actual package being built (ie, emacs in
this case) that are almost always (?) to blame.

Maybe it's better not to say anything about the likely cause, if it's
hard to figure out.