error in diff in 1.2_STABLE processing arguments

[Yury Tarasievich]

diff doesn't tolerate second filename being ``-''  (or rather it is about line 
ending in ``-'').

If f1 and f2 are files,

cat f2 | diff - f1
  is fine 

cat f2 | diff f1 -
 gives (unexpected) error.

-regards