build failure with recent cmake

[Oswald Buddenhagen]

moin,

kdelibs fails to compile for me, suddenly not finding libz and libpng.
the following message may be indicative for the problem:

-- REQUIRED_VARS  (missing:  VERSION_VAR)
-- Could NOT find PNG  (missing:  PNG_LIBRARY PNG_PNG_INCLUDE_DIR)

that happens with the cmake release branch from git. running
  git checkout b6c8d8f8^ && make install
fixes the problem. i haven't tried to verify whether this merge is
actually to blame.