Make CTest.UpdateGIT robust to user git config

Part of this test does "git pull" on a dirty work tree.  We need to make
sure that 'branch.master.rebase' is false for the test repository.
Otherwise if it is true in the user configuration then pull will refuse
to rebase and the test will fail.

Tests/CTestUpdateGIT.cmake.in

@@ -135,6 +135,13 @@ run_child(
   COMMAND ${GIT} reset --hard master~2
   )
 
+# Make sure pull does not try to rebase (which does not work with
+# modified files) even if ~/.gitconfig sets "branch.master.rebase".
+run_child(
+  WORKING_DIRECTORY ${TOP}/user-source
+  COMMAND ${GIT} config branch.master.rebase false
+  )
+
 # Create a modified file.
 modify_content(user-source)