This completes the changes required for #221.

Adjusts for the fact that the old task.is_waiting() test used to return
True for retrying tasks as well as ones in the 'waiting' state. Now we
do direct tests on the state value, so must check for 'retrying' too
where appropriate.
Fixed a trivial typo that only affected task locking.

The cylc lockserver is currently only used at NIWA.
Trivial doc typo fix.
Minor documentation change.
Added www links to the doc index.
Added .tex sources as deps in doc Makefile.

This allows re-make after changes to the source, without deleting the
generated documents.
Merge pull request #228 from hjoliver/doc-makefile-deps

Added .tex sources as deps in doc Makefile.
Merge pull request #225 from hjoliver/221-follow-up

This completes the changes required for #221.