KDELibs4Support fails to install on Windows if DocBookXML4 absent

[Nicolás Alvarez]

Hello,

Currently KDELibs4Support fails to install on Windows. It gives the
following error:

CMake Error at src/cmake_install.cmake:264 (file):
  file RELATIVE_PATH must be passed a full path to the file:
  searched_dir-NOTFOUND
Call Stack (most recent call first):
  cmake_install.cmake:115 (include)

The problem is in src/CMakeLists.txt:653. It tries to use
DocBookXML4_DTD_DIR unconditionally, even though DocBookXML4 is an
optional package so it may not be found (and it is in fact not present
in the current Windows setup).

Could some CMake/docbook expert take care of it? This is only one of
two problems preventing KDELibs4Support from working on Windows, and
the other problem isn't really in KDELibs4Support :)

-- 
Nicolás