Merge branch 'difftool-no-index-extra'

This patch addresses the segmentation faults in `git difftool --no-index
--dir-diff`: surprisingly, those two options don't make no sense
together.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

builtin/difftool.c

@@ -735,7 +735,8 @@ int cmd_difftool(int argc, const char **argv, const char *prefix)
 		setup_work_tree();
 		setenv(GIT_DIR_ENVIRONMENT, absolute_path(get_git_dir()), 1);
 		setenv(GIT_WORK_TREE_ENVIRONMENT, absolute_path(get_git_work_tree()), 1);
-	}
+	} else if (dir_diff)
+		die(_("--dir-diff is incompatible with --no-index"));
 
 	if (use_gui_tool && diff_gui_tool && *diff_gui_tool)
 		setenv("GIT_DIFF_TOOL", diff_gui_tool, 1);