Fix install and unnecessary string copy

- Fix the following issue when running "make install"
  https://github.com/ceres-solver/ceres-solver/issues/527

- Fix error that CeresCodeGeneration.cmake was not found
  after instalation. Issue:
  https://github.com/ceres-solver/ceres-solver/issues/561

- Removes the unnecessary string copy during code generation

Change-Id: I01963d01da6a9c4557aad6f89831647c1a149e38

CMakeLists.txt

@@ -772,7 +772,7 @@ install(FILES "${Ceres_BINARY_DIR}/CeresConfigVersion.cmake"
         DESTINATION ${RELATIVE_CMAKECONFIG_INSTALL_DIR})
 
 # Install codegen cmake scripts
-install(FILES "${Ceres_SOURCE_DIR}/cmake/codegen_include.h.in"
+install(FILES "${Ceres_SOURCE_DIR}/cmake/codegen_include.inc.in"
               "${Ceres_SOURCE_DIR}/cmake/generate_code_for_functor.cc.in"
               "${Ceres_SOURCE_DIR}/cmake/CeresCodeGeneration.cmake"
         DESTINATION ${RELATIVE_CMAKECONFIG_INSTALL_DIR})

cmake/CeresConfig.cmake.in

@@ -168,7 +168,7 @@ find_dependency(Threads)
 
 # Import code generation functions s/t they are available for use in client code
 # if find_package(Ceres) is successful.
-include(CeresCodeGeneration.cmake)
+include(CeresCodeGeneration)
 
 # Eigen.
 # Flag set during configuration and build of Ceres.

cmake/generate_code_for_functor.cc.in

@@ -20,7 +20,7 @@ int main() {
     std::cerr << "Could not open file " << output_file << std::endl;
     return EXIT_FAILURE;
   }
-  for (auto line : lines) {
+  for (const auto& line : lines) {
     stream << line << std::endl;
   }
   return EXIT_SUCCESS;