[PATCH 0/4] emacs: Add "View graph" action to graph popup.

[Alex Kost]

This patchset adds "View graph" action to 'guix graph' popup (i.e., to
"M-x guix RET G").  By default the graph (png) will be opened in Emacs,
but this can be changed by setting 'guix-find-file-function' variable.
For example, I prefer to open png-files in sxiv, so I use:

(setq guix-find-file-function 'org-open-file)

and I have ("\\.png\\'" . "sxiv %s") element in my 'org-file-apps' var.

If you don't like png, you can set 'guix-dot-default-arguments' and
'guix-dot-file-name-function'.

[PATCH 1/4] emacs: Add code to pipe guix output to external program.
[PATCH 2/4] emacs: Add code to run 'dot' program.
[PATCH 3/4] emacs: Allow to choose 'find-file' function.
[PATCH 4/4] emacs: Add "View graph" action to graph popup.