New grid item added

[Damon Chaplin <damon karuna eclipse co uk>]

I've just added a new grid item to svn.

The properties are:

  x, y, width, height  - the area the grid covers. grid lines are
                         clipped to this.
  x_step, y_step       - the distance between grid lines.
  x_offset, y_offset   - the distance to the first grid lines.

  horz-grid-line-width - the width of the grid lines.
  vert-grid-line-width   (defaults to the item's line width)

  horz-grid-line-pattern - the color/pattern to paint the grid lines
  vert-grid-line-pattern   (these default to the item's stroke color)

  border-width         - the width of the border around the grid.
                         (outside the grid's x, y, width & height)
  border-pattern       - the color/pattern to paint the border.

  vert-grid-lines-on-top - TRUE if vertical lines are on top.
  
It also has the normal convenience properties for the patterns, i.e.
XXX-color, XXX-color-rgba and XXX-pixbuf.


Let me know if I've missed any essential features.

Note that the grid currently clips to the x, y, width & height
properties, and the border is tight around that area. So if x_offset or
y_offset is 0 then half the grid lines get clipped. I'm not entirely
sure this is the correct thing to do. Possibly not.

Damon