Bug 1025727 - [email/cronysync] Failsafe abort/window.close after (multiple?) failed cronsync(s)

From master commit e64d7adf507d0f0164988257d30600499b1e5776
Merge pull request #21070 from jrburke/bug1025727-v1.3-email-cronsync-failsafe

Bug 1025727 - [email/cronysync] Failsafe abort/window.close after (multiple?) failed cronsync(s) r=mcav a=bajaj