Fix XBM to parse #defines correctly.

I found this XBM file on the net:

/* (circles.xbm) */
#define icon_width 16
#define icon_height 16
#define icon_x_hot 4
#define icon_y_hot 4
static char icon_bits[] = {
  0x00, 0x00, 0x7c, 0x00, 0x82, 0x00, 0x82, 0x00,
  0x82, 0x00, 0x82, 0x00, 0x82, 0x00, 0x7c, 0x3e,
  0x00, 0x41, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80,
  0x80, 0x80, 0x80, 0x80, 0x00, 0x41, 0x00, 0x3e };

I had to change the parsing of #define to get it to load.