[release] "make install" needs a run of make doc first

I was a bit surprised that a simple make install fails since the pdf files are not built without running "make doc" before:

CMake Error at doc/comm/cmake_install.cmake:36 (file):
  file INSTALL cannot find
  "/home/mblatt/src/dune/dune-2.7/dune-common/build-dist/doc/comm/communication.pdf".
Call Stack (most recent call first):
  doc/cmake_install.cmake:43 (include)
  cmake_install.cmake:68 (include)

Is that expected? If it is we should probably mention it somewhere (I have neither found a comment in INSTALL nor on the website).