Since 0.8.1 we return 0, even if no changes are found.
I just hit this when I wanted to run tests only when pulling yields new changesets.

My suggestion:
rc=255 on errors
rc=0 if ok
(until here it is compatible with the current behaviour)

rc=1 if there was no error, but no real action was done.
As this might be annoying for regular use, maybe only activate this feature when
a certain switch is used, e.g. --report?