"cylc -v" for a repo returned nothing if not in repo to dir.

I hadn't noticed as I normally work from within my clone.
Bug fix doc/Makefile for missing latex commands.

The generated dependencies ('html', 'pdf') were not being used properly,
resulting in a fatal error if htlatex was not installed.
Moved some gtk imports down to avoid display errors.

Running 'make' on a remote post-commit hook failed with "can't open
display" errors from a few commands - which this fixes.
Merge pull request #272 from hjoliver/no-X-display-for-help

Moved some gtk imports down to avoid display errors.
Merge pull request #270 from hjoliver/fix-doc-makefile-deps

Bug fix doc/Makefile for missing latex commands.
Merge pull request #269 from hjoliver/bug-fix-get-repo-version

"cylc -v" for a repo returned nothing if not in repo to dir.