fix for finding Eigen

Former-commit-id: 6a87b5f43613515c65aac5afb9615d177c5addc5

tutorial/cmake/FindEIGEN.cmake

@@ -66,6 +66,9 @@ else ()
       ${CMAKE_INSTALL_PREFIX}/include
       ${KDE4_INCLUDE_DIR}
 	  ${PROJECT_SOURCE_DIR}/../../../Eigen
+    ${PROJECT_SOURCE_DIR}/../../../external/nanogui/ext/eigen/
+    ${PROJECT_SOURCE_DIR}/../../external/nanogui/ext/eigen/
+    ${PROJECT_SOURCE_DIR}/../external/nanogui/ext/eigen/
 	  $ENV{DevLibraries}/Eigen
       PATH_SUFFIXES eigen3 eigen
     )