Allotment styling mismatch at metatile boundaries

[matkoniecz]

for example http://www.openstreetmap.org/?mlat=50.08878&mlon=19.86328#map=18/50.08878/19.86328

closely related to #299

[pnorman]

#97 too

[pnorman]

Current image size is 6 px, so we'll have to change that to a power of two.

[matthijsmelissen]

Does that mean that metatiles of size 840=2_3_4_5_7 would have been easier? :)

[pnorman]

Rather than 2304?