Kwiver exported targets don't use target usage requirements

[mwoehlke-kitware]

If I want to use Kiwver in my own project, I have to do this:

include_directories(${KWIVER_INCLUDE_DIRS})

This is sub-optimal since CMake 2.8.10. Kwiver's exported targets should have INTERFACE_INCLUDE_DIRECTORIES set so that all I have to do is link to the library.