Multi-line text alignment

Added tests for multi-line text line placement: each line of text should be placed directly above the next, according to the "justify-alignment" property. As could already be seen in the "lines-5" test case, this sometimes wasn't happening on sinusoidal lines. This PR adds a new test case specifically for looking at multi-line text alignment, and includes a patch which fixes the issue.

The patch changes the behaviour enough to alter the output of two tests; updates for those reference files are included and have been visually checked, although more checking is always welcome. The "lines-5" case seems improved, but the "lines-offset" is not so clear whether it's an improvement or not.