Always log if we get an unexpected conflict and have to retry

Signed-off-by: David Scott <dave.scott@citrix.com>
Improve the 'origin' messages.

* Avoid saying 'merge': irmin will say this when it makes a merge commit
* Make the first line summarise the operation (eg read /foo = bar)

Signed-off-by: David Scott <dave.scott@citrix.com>