[Tilesathome] Striped rendering is back

[Matthias Julius]

I have just commited my new implementation of the striped rendering to
the _unstable client.  This is now optional and configurable.

The client now knows a new config parameter RenderStripes.  When set
to 0 (which is the default) each zoom level is rendered in one go.  If
RenderStripes is set to a positive number this number is the zoom
level (relative to the top level in the tileset starting with 0) from
which on the rendering is done in stripes.  E.g. if set to 1 all zoom
levels are rendered in stripes.  This is the previous behavior.  If
set to 5, level number 5 (corresponding to z17 on a z12 tileset) will
be rendered in 4 stripes.

Matthias