Arnaus Gelas' patch to move to Ctest

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 70336ae..ed7dbc1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -36,7 +36,7 @@
 
 PROJECT(CERES C CXX)
 
-ENABLE_TESTING()
+INCLUDE(CTest)
 
 # SuiteSparse
 OPTION(SUITESPARSE

internal/ceres/CMakeLists.txt

diff --git a/internal/ceres/CMakeLists.txt b/internal/ceres/CMakeLists.txt
index f02db23..7891138 100644
--- a/internal/ceres/CMakeLists.txt
+++ b/internal/ceres/CMakeLists.txt
@@ -139,8 +139,7 @@
 
 TARGET_LINK_LIBRARIES(ceres ${CERES_LIBRARY_DEPENDENCIES})
 
-OPTION(BUILD_TESTS "Build the unit tests." ON)
-IF (BUILD_TESTS)
+IF (BUILD_TESTING)
   ADD_LIBRARY(gtest gmock_gtest_all.cc gmock_main.cc)
   ADD_LIBRARY(test_util test_util.cc)
   TARGET_LINK_LIBRARIES(gtest ${GFLAGS_LIB} ${GLOG_LIB})
@@ -193,4 +192,4 @@
   CERES_TEST(unsymmetric_linear_solver)
   CERES_TEST(visibility)
   CERES_TEST(visibility_based_preconditioner)
-ENDIF (BUILD_TESTS)
+ENDIF (BUILD_TESTING)