[Tilesathome] Rendering tiles west of Greenwich and/or south of the equator.

[Maarten Deen]

When I render a tile with negative coordinates, I get a lot of messages like
Argument "-3,864255" isn't numeric in addition (+) at orp.pl line 306.
Argument "-3,776559" isn't numeric in addition (+) at orp.pl line 306.
Argument "-38,583984" isn't numeric in subtraction (-) at orp.pl line 308.
Argument "-38,496094" isn't numeric in subtraction (-) at orp.pl line 308.

The resulting tile seems to be ok, which seems a little strange given all these 
errors.

Maarten