[tx] '-altLayer' option not working

[miguelsousa]

The output of tx -6 -altLayer background tx_data/input/altlayer.ufo/ should be,

## glyph[tag] {name,encoding,path}
glyph[0] {foo,-,
  500 width
  230 322 move
  290 322 340 371 340 430 curve
  340 489 290 537 230 537 curve
  169 537 119 489 119 430 curve
  119 371 169 322 230 322 curve
  endchar}

instead of

## glyph[tag] {name,encoding,path}
glyph[0] {.notdef,-,
  500 width
  endchar}
glyph[1] {foo,-,
  500 width
  70 384 move
  260 384 line
  260 586 line
  70 586 line
  endchar}