Merge branch 'jc/add-i-use-builtin-experimental'

The "add -i/-p" machinery has been written in C but it is not used
by default yet.  It is made default to those who are participating
in feature.experimental experiment.

* jc/add-i-use-builtin-experimental:
  add -i: use the built-in version when feature.experimental is set

builtin/add.c

@@ -192,9 +192,15 @@ int run_add_interactive(const char *revision, const char *patch_mode,
 	int use_builtin_add_i =
 		git_env_bool("GIT_TEST_ADD_I_USE_BUILTIN", -1);
 
-	if (use_builtin_add_i < 0)
-		git_config_get_bool("add.interactive.usebuiltin",
-				    &use_builtin_add_i);
+	if (use_builtin_add_i < 0) {
+		int experimental;
+		if (!git_config_get_bool("add.interactive.usebuiltin",
+					 &use_builtin_add_i))
+			; /* ok */
+		else if (!git_config_get_bool("feature.experimental", &experimental) &&
+			 experimental)
+			use_builtin_add_i = 1;
+	}
 
 	if (use_builtin_add_i == 1) {
 		enum add_p_mode mode;