Hi,

There is already support for random X-Face in Gnus.  This patch adds
support for png faces as well.  Further, support to omit certain faces
in a dir is added.  It works nicely e.g. for posting-styles.

I'd welcome any feedback.

I have mainly tested with png faces as the suggested way of producing
X-Faces (e.g. gnus-convert-pbm-to-x-face-command) didn't work as
expected on my system (with compface 1.5.2 and netpbm 10.61.0).

I have signed copyright paper to Emacs.

–Rasmus