This is how DETH deals with X Texture Alignment:

   1      2      3      4        Selection Order
x----->x----->x----->x----->
  1st    1st    1st    1st       SideDef DETH is going to align to

   4      3      2      1    
x----->x----->x----->x----->
  2nd    2nd    2nd    2nd  

   1      2       3     4  
x----->x----->x<-----x----->
  1st    1st     2nd   1st

   4      3      2      1  
x<-----x----->x<-----x----->
  1st    2nd    1st    2nd


So as you can see, DETH works out which SideDef it has to work on, no need 
for separate menu options.

The general rule to remember is that DETH will always align the SideDef to the
right of the selection order.

Alignment is texture based and will check for different textures, you can also
input an initial offset.

It also works if the sidedef doesn't have any textures, and will also align on 
the Upper and Lower textures. - so no more barfing!