Hello,

While combing through a collection of files, I noticed that whenever I 
called diff with both --ignore-trailing-space and 
--ignore-tab-expansion, the latter option was seemingly ignored. 
Initially I was worried that combining them was’t supported at all, 
even though the documentation suggested nothing of the sort. So I dug 
into the source code to see whether this was a feature omission or a 
bug. Half an hour later, I had a patch ready. Attached.

I don’t believe the patch needs copyright assignment, given that it 
changes just two lines and adds one. Though I figure writing some tests 
to cover this case is in order, which I did not do.

—f