Anchors not found

With Sphinx upgraded to 1.2b1, anchors are now systematically checked by the `linkcheck` target. This PR fixes the broken anchors and should turn the OMERO merge doc job green again.

If testing locally, environment variables should be configured as in the jobs, see
http://hudson.openmicroscopy.org.uk/view/Docs/job/OMERO-docs-merge-stable/305/parameters/?
or 
http://hudson.openmicroscopy.org.uk/view/Docs/job/OMERO-docs-release-stable/62/parameters/?