Todo for Graph-Easy-As_svg

Output bugs:

* a graph border of double is rendered as single
* Anon groups should not have a border
* Borders on nodes/graph are placed on the path center. Instead they should
  be inside the shape, aka moved BORDER-WIDTH/2 to the inside.
* Rotated nodes:
  + Node texts are moved wrongly on rotated nodes (their new
    center should rotate along with the shape)
  + do not increase the graph size, so corners might get cut off
  + the label text is not rotated with the rest of the shape
* implement border- and edge-style: wave
* _text_length() could be more accurate
* edges with style "double" have wrong corner pieces
* wide and broad self-loops are too small and the line must be moved
* support different edge starting point styles ala:

  ----->  |----->  o----->  +----->  *----->  >>----->

Shorter output:

* instead of rendering individual edge cells, we should create
  one path, this would allow better rendering of non-solid
  edges, like dashed or dotted ones
* put the stroke-width and stroke on the <g class="edge"> instead on
  each <line>
* merge all group cells together to create a minimum number of rectangles
  to render
* font-family and font-size are output needless even when they are the
  default values

Browser-specific woes:

* Firefox 1.5 gets tspan with 'x="..." dy="1em"' wrong
* Firefox 1.5 seems to ignore text-decoration on <text>
* Batik 1.5.1 has problems with 'font-size="12px"' on <text>