Finished release 1.0.3.
Post Release: Version 1.0.3 -> 1.0.4dev.
Change SR relname from 'sr' to 'srs'.

I just noticed this mistake. I haven't seen any issues caused by this
problem. It may cause SRs to not be removed when incremental modeling
noticed that an SR has been removed in XenServer.
Fix "argument of type 'NoneType' is not iterable".

It appears that in some cases a model event will occur that doesn't have
a snapshot or a parent. I haven't been able to isolate the case where
this occurs, but the safe thing to do is ignore the update and catch any
resulting drift in the period full remodel.

Fixes ZEN-14856.
Merge pull request #10 from zenoss/feature/ZEN-14856

Please review branch feature/ZEN-14856
Release: Version 1.0.4dev -> 1.0.4.
Document 1.0.4 changes.
Finished release 1.0.4.