Better error message if one forgets to set KDEDIR variable

[Mario Fux]

Good morning

Yesterday evening I had a problem which dfaure helped me to solve. I forgot to 
(re)set the KDEDIR variable and thus got errors like:

-- ************** ecm_version() is obsolete, use ecm_set_version_variables() 
instead
-- file RELATIVE_PATH relInstallDir /lib/i386-linux-gnu/cmake/itemmodels 
CMake Error at /usr/local/share/extra-cmake-
modules-0.0.3/modules/ECMQtFramework.cmake:125 (file):
  file RELATIVE_PATH called with incorrect number of arguments
Call Stack (most recent call first):
  tier1/itemmodels/CMakeLists.txt:15 (include)

Of line of the aboves is the debug line dfaure sent me as a patch. See [1] for 
the whole output of cmake.

Here is my cmake line:
/home/fmario/devel/KDE/cmake-build/bin/cmake ../kdelibs -
DCMAKE_INSTALL_PREFIX=$KDEDIR -DCMAKE_BUILD_TYPE=debugfull

After resetting KDEDIR to the correct directory everything worked fine but 
dfaure told me to write this to the buildsystem list and thus Alex to mention 
that there should be a better error message for this problem.

Oh and please CC: me as I'm not subscribed to this list.

thx
Mario

[1] http://paste.kde.org/426248/