Do not duplicate code from ocitysmap
Do not duplicate code from ocitysmap

This patch imports one module from ocitysmap to compute the extension
of a bbox, instead of duplicating the code of the routine. This patch
relates to patch ocitysmap's 78c067e3ece79d62e87893c6747b6c609571c6bb.

hholzgra/maposmatic,hholzgra/maposmatic,wonderchook/MapOSMatic,hholzgra/maposmatic,maposmatic/maposmatic,hholzgra/maposmatic,maposmatic/maposmatic,maposmatic/maposmatic,hholzgra/maposmatic,wonderchook/MapOSMatic,maposmatic/maposmatic