Some EGCs are more than 2 columns (wcwidth() never returns more than 2, so far as i can tell, but when multiple characters combine, we use the sum). An example would be ကြေ (Myanmar) which occupies three columns over the course of three characters. Track the width (biased by 1) in cell->width, taking over 8 bits from cell->reserved. Use this width in rasterization. Closes#1203.