On closer inspection I realized that API functions are removed from
  libtiff; shouldn't we bump it's major number?

If they only showed up in pkgsrc libtiff during the interval when it
(brokenly) had C++ stuff in the base library, and if further they
really are C++ functions (as opposed to C functions implemented in
C++), then I'd argue that the harm of version bumping outweighs the
benefit to things that managed to link agains the c++ libtiff during
the last few weeks.

-- 
        Greg Troxel <gdt@ir.bbn.com>