In Term_pict_cocoa(), step through the passed in arrays in increments of the tile...

In Term_pict_cocoa(), step through the passed in arrays in increments of the tile width scaling (i.e. 2 in big tile mode; 1 otherwise).  Does not matter in the current configuration, with always_pict off, but would matter if always_pict was on or if the core terminal code was modified to pass more than one tile at a time when higher_pict is on.