Bug 1039007 - [email/backend] Do not invoke operation callbacks until after any associated saves have safely hit the disk. r=mcav

landing https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/323
Merge pull request #21967 from asutherland/email-op-callbacks-after-save

Bug 1039007 - [email/backend] Do not invoke operation callbacks until after any associated saves have safely hit the disk. r=mcav