autobuilder: Support push notifications via files-in-directory
autobuilder: Support push notifications via files-in-directory

Pending some messaging system integration, this is a low-tech solution
that will get us a lot closer to having the build system be able to
keep up with GNOME commits.

GNOME/gnome-ostree,vrutkovs/vrutkovs.github.io,djdeath/gnome-ostree,GNOME/gnome-ostree,djdeath/gnome-ostree,chergert/gnome-continuous,vrutkovs/vrutkovs.github.io,GNOME/gnome-ostree,chergert/gnome-continuous,djdeath/gnome-ostree,vrutkovs/vrutkovs.github.io,chergert/gnome-continuous