Merge pull request #110 from fgp/fix-eigen3-include-path

Use include_directories() instead of add_definitions() to set EIGEN3_INCLUDE_DIR

CMakeLists.txt

@@ -494,7 +494,8 @@ if (NOT EIGEN3_INCLUDE_DIR)
         message(FATAL_ERROR "Eigen3 library not found. Either install it or rerun cmake with -DEIGEN3_INCLUDE_DIR=<installed_eigen3_dir>")
     endif()
 endif()
-add_definitions("-I${EIGEN3_INCLUDE_DIR} -DUSE_EIGEN3")
+include_directories(AFTER SYSTEM ${EIGEN3_INCLUDE_DIR})
+add_definitions("-DUSE_EIGEN3")
 add_subdirectory(model)
 add_subdirectory(gsl)
 add_subdirectory(alignment)