Only load Session on the client.

Fixes 751.
Add History.md note about Session.
docs link fixes from check_links()
Return multiple cursors from publish function.
Review of PR #716 (multi-cursor publish).

- History.md update

- tweak docs

- refactor the "one per collection" check

- make errors into internal errors.  Programming errors like returning the wrong
  type from a function on the server don't need to be reported to the client.
Merge PR 716 into devel: returning multiple cursors from publish.
Update license file for new npm modules.
C.find(q, {reactive: false}).observe() should only produce initial adds.

Fixes #771.
Make eventData an empty object if no data context is found.

This prevents the thisArg from getting set to `window` if eventData is
undefined.

See:
http://stackoverflow.com/questions/15137206/the-context-of-this-in-meteor-template-event-handlers-using-handlebars-for-te/15149650#15149650
History.md update
Editing pass on History.md
observe changes tests no longer leak observe handles
Don't leak a LiveResultsSet on erroneous recursive observe.
Stop keeping around so many subscriptions when we are done testing
Merge branch 'devel' into appcache