Unregister sessions from server when their heartbeats time out.
Fix 0.8.1 regression in ROOT_URL with path

Fixes #2109.
Add credential secret argument to `retrieveCredential` functions.

Fixes #2118.
Unregister sessions from server when their heartbeats time out.

Conflicts:
	History.md
Update History.md
Make a History sentence more sentence-y
Better error when releasing an unbuilt git sha
docs: turn off appcache on safari

Turns out AppCache on Safari 7 is totally broken (see
http://stackoverflow.com/questions/22888945/safari-7-application-cache-does-not-work).
This, combined with our "reload if you can't load CSS or JS" strategy for
multi-server deploy causes infinite reloads in some cases.

Hopefully this will resolve the sporadic complaints we get
from some users about infinite reloads.
Add an XXX about only_credential_secret_for_test
Update banner and notices
Update docs to 0.8.1.2
Update examples to 0.8.1.2
Merge branch 'release-0.8.1.2'
Merge branch 'master' into devel
Document UI.getElementData

While doing this, I realized that this function
can be called on text nodes as well, so it's probably
better named UI.getNodeData?
Remove statement about Rails and Django

Fixes #2142.  Apparently Django doesn't work precisely this way.
Clean up event handlers (untested)

Needs manual testing and then a unit test (that exercises multiple eventTypes as well).
Fix typo in DomRange event handler cleanup
Add a test for cleaning up event handlers when template is destroyed
Merge branch 'event-cleanup-cherrypick' into devel