#27 if the last number of geotransform is -1 (bottom-up), flip GCPs given by metadata
#27 remove unnecessary comment lines
#27 remove geotransform and set BOTTOMUP option in nansat.export()
#27 Undo 1b9a224. Flip GCPs in vrt._add_gcp_metadata(), if bottomup is False.
#27 if bottoum true: image is written with bottom on top; flip option removed from export, export_band
#27 merge issue27 into develop