Add -iquote support

[Mark Mitchell]

Zack Weinberg wrote:

> I would like to add to this discussion the observation that I don't
> believe anyone ever uses -I- precisely because it disables searching
> the directory-of-the-current-file; this tends to break system
> headers.  I would seriously consider a patch that removed that mode
> entirely.

I'd have fewer reservations about that, although it would break 
backwards compatibility....

-- 
Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com