CMakeLists: use find_package Eigen3

Instead of hardcoding the Eigen3 path which only works on Mac, use
find_package(Eigen3).

EKF/CMakeLists.txt

@@ -37,12 +37,12 @@ project (ECL CXX)
 set(CMAKE_BUILD_TYPE Release)
 set(CMAKE_CURRENT_SOURCE_DIR ./)
 set(CMAKE_CXX_FLAGS "-DPOSIX_SHARED")
-set(EIGEN3_INCLUDE_DIR "/usr/local/include/eigen3/")
 
-IF( NOT EIGEN3_INCLUDE_DIR )
-	MESSAGE( FATAL_ERROR "Please point the environment variable EIGEN3_INCLUDE_DIR to the include directory of your Eigen3 installation.")
-ENDIF()
-INCLUDE_DIRECTORIES ( "${EIGEN3_INCLUDE_DIR}" )
+find_package(Eigen3 REQUIRED)
+
+if( NOT EIGEN3_INCLUDE_DIR )
+	message( FATAL_ERROR "Eigen3 not found.")
+endif()
 
 if( NOT EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/../matrix/.git" )
 message( SEND_ERROR "The git submodules are not available. Please run
@@ -54,9 +54,9 @@ include_directories(
 	./
 	../
 	../matrix
-	EIGEN3_INCLUDE_DIR
+	${EIGEN3_INCLUDE_DIR}
 )
-set(SRCS 
+set(SRCS
 	estimator_interface.cpp
 	ekf.cpp
 	ekf_helper.cpp