libxml++: fix unpackaged files

* fixes:
libxml++-2.35.3: libxml++: Files/directories were installed but not shipped
  /usr/share/devhelp
  /usr/share/devhelp/books
  /usr/share/devhelp/books/libxml++-2.6
  /usr/share/devhelp/books/libxml++-2.6/libxml++-2.6.devhelp2
  /usr/lib/libxml++-2.6
  /usr/lib/libxml++-2.6/include
  /usr/lib/libxml++-2.6/include/libxml++config.h

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>