Flexible shared assets path.
Merge pull request #403 from spectator/master

Flexible shared assets prefix
Issue #441, when asked to teardown the connection to a server, if the connection is already dead recent Net::SSH versions will throw Net::SSH::Disconnected so handle that too
Merge pull request #442 from willbryant/master

Handle Net::SSH::Disconnected like IOError in teardown_connections_to
More changelog, close to shippign 2.15.0
Support JSON manifests and manifests with randomized filenames
Don't assume we have a manifest in the updaate_asset_mtimes task, because it's run before the precompile task
Sync randomized manifest filenames between servers
Cache manifest path
Check for assets:precompile:nondigest rake task before invoking it during rollbacks, because Rails 4 does not have nondigest assets