Allow to configure different aspect ratios of tiles.

For example for Plate Carree which has a 2x1 ratio
or OSGB which can use a 1x2 ratio
Add a OSGB36 projection to renderd

Add some tests for tile number to projected coordinate bounds
Try and be more helpful with error messages if an exception is thrown while saving.

Also don't exit renderd entirely if an exception is thrown.
Try and be more helpful with error messages if an exception is thrown while saving.

Also don't exit renderd entirely if an exception is thrown during saving.
Merge branch 'master' of git://github.com/openstreetmap/mod_tile
Use Stack in the munin graph of queue_time
Fix sending back NotDone from renderd immediately if request doesn't fit into a rendering queue

RenderPrio, Render and RenderLow queues each only have a size of 32 entries. If these are full,
then requests overflow into the dirty queue. If this happens, renderd should send the NotDone
back immediately so that mod_tile doesn't wait for potentially a long time.

This however only worked for Render requests, but not RenderPrio or RenderLow. This patch fixes this.
Set min value of 0 for munin graph render time spent by queue