enable optional build for the docs subdir
enable optional build for the docs subdir

svn path=/trunk/KDE/kdepim/; revision=813684

lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi,lefou/kdepim-noakonadi