svn 1350 "fix dyadic ¨ with 1-element arguments"

[Bill Heagy]

Before this change:
      ⍴⍴(1 2)+¨⊂ 3 4 5
1
      ⍴⍴(,2)+¨⊂ 3 4 5
1
which is what I expected.

After the change:
      ⍴⍴(1 2)+¨⊂ 3 4 5
1
      ⍴⍴(,2)+¨⊂ 3 4 5
0

I don't know if the change for a 1-element vector compared to, say, a 
2-element vector was intended.  (debian, various versions)