index: Index MusicBrainz album IDs from music files.

Index "MusicBrainz Album ID" ID3v2 frames as
"musicbrainzalbumid" media tags to facilitate downloading
cover art from coverartarchive.org.

Change-Id: Ie81017dd6f76ec355ee0d1daedfb7180cb70ad59
devcam review: submit changes for review

Context: http://camlistore.org/issue/408

Change-Id: I587de65c9dc8d87c02541096e1f4f7765e644962
Merge "devcam review: submit changes for review"
Merge "index: Index MusicBrainz album IDs from music files."
importer: periodic import

Change-Id: Id324890833cb8f5672a0fa3a8df342dc05e6298c
Merge branch 'master' of https://camlistore.googlesource.com/camlistore
pkg/test: move importers' fakeTransport to test.NewFakeTransport

Change-Id: Iadefb6358983c0d479b269de47d368abf5e0c93b
test: add forgotten file from 94ab7a8

Change-Id: Ied44257d300d55b6b65daedf8f8ebd1a407d53a9