Bug 814257 - [email] Move back-end into worker thread (speculative). groundwork, use node shims instead of mozTCPSocket. r=asuth, a=gal

https://bugzilla.mozilla.org/show_bug.cgi?id=814257
Land https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/122
Merge pull request #8066 from asutherland/email-land-imap-use-tcp-shim

Bug 814257 - [email] Move back-end into worker thread (speculative). groundwork, use node shims instead of mozTCPSocket. r=asuth, a=gal