KDE4_INCLUDES also contains Qt includes required by KDE.
See FindKDE4Internal.cmake for more details.

Fixes Gentoo bug #510500.
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -55,7 +55,7 @@
 )
 
 INCLUDE_DIRECTORIES(
-    ${KDE4_INCLUDE_DIR}
+    ${KDE4_INCLUDES}
     ${QT_INCLUDE_DIR}
     ${Boost_INCLUDE_DIRS}
     ${CMAKE_CURRENT_BINARY_DIR}/src