It is useful for us to reference system-wide include files. For example, we would like to override the aegir makefile in our own distribution, this way:
includes[aegir] = "/var/aegir/.drush/provision/aegir.make"
or, with the debian package:
includes[aegir] = "/usr/share/drush/commands/provision/aegir.make"
Neither works. The documentation says the path is "relative" but doesn't explicitely say that absolute paths are forbidden. I tried an absolute path, thinking myself very smart, but that didn't work either:
includes[aegir] = "../../../../usr/share/drush/commands/provision/aegir.make"
... even though that actually works on the commandline.
This needs to be clarified in the documentation or clearly allowed. I would like to see this implemented.