CTest: Fix ctest_update with 'HEAD' file in source tree

Add the '--' command-line separator to make the HEAD reference
unambiguous.  Extend the CTest.UpdateGIT test to cover this case.

Source/CTest/cmCTestGIT.cxx

@@ -68,7 +68,7 @@ std::string cmCTestGIT::GetWorkingRevision()
 {
   // Run plumbing "git rev-list" to get work tree revision.
   const char* git = this->CommandLineTool.c_str();
-  const char* git_rev_list[] = {git, "rev-list", "-n", "1", "HEAD", 0};
+  const char* git_rev_list[] = {git, "rev-list", "-n", "1", "HEAD", "--", 0};
   std::string rev;
   OneLineParser out(this, "rl-out> ", rev);
   OutputLogger err(this->Log, "rl-err> ");
@@ -639,7 +639,7 @@ void cmCTestGIT::LoadModifications()
   this->RunChild(git_update_index, &ui_out, &ui_err);
 
   // Use 'git diff-index' to get modified files.
-  const char* git_diff_index[] = {git, "diff-index", "-z", "HEAD", 0};
+  const char* git_diff_index[] = {git, "diff-index", "-z", "HEAD", "--", 0};
   DiffParser out(this, "di-out> ");
   OutputLogger err(this->Log, "di-err> ");
   this->RunChild(git_diff_index, &out, &err);

Tests/CTestUpdateGIT.cmake.in

@@ -76,6 +76,8 @@ run_child(WORKING_DIRECTORY ${TOP}/module
 # Import initial content into the repository.
 message("Importing content...")
 create_content(import)
+file(WRITE ${TOP}/import/HEAD "HEAD\n")
+file(WRITE ${TOP}/import/master "master\n")
 
 # Import the content into the repository.
 run_child(WORKING_DIRECTORY ${TOP}/import
@@ -157,19 +159,19 @@ update_content(user-source files_added files_removed dirs_added)
 if(dirs_added)
   run_child(
     WORKING_DIRECTORY ${TOP}/user-source
-    COMMAND ${GIT} add ${dirs_added}
+    COMMAND ${GIT} add -- ${dirs_added}
     )
 endif()
 run_child(
   WORKING_DIRECTORY ${TOP}/user-source
-  COMMAND ${GIT} add ${files_added}
+  COMMAND ${GIT} add -- ${files_added}
   )
 run_child(
   WORKING_DIRECTORY ${TOP}/user-source
-  COMMAND ${GIT} rm ${files_removed}
+  COMMAND ${GIT} rm -- ${files_removed}
   )
 run_child(WORKING_DIRECTORY ${TOP}/user-source/module
-  COMMAND ${GIT} checkout master
+  COMMAND ${GIT} checkout master --
   )
 run_child(
   WORKING_DIRECTORY ${TOP}/user-source