Merge branch 'jk/daemon-interpolate' into maint

The "interpolated-path" option of "git daemon" inserted any string
client declared on the "host=" capability request without checking.
Sanitize and limit %H and %CH to a saner and a valid DNS name.

* jk/daemon-interpolate:
  daemon: sanitize incoming virtual hostname
  t5570: test git-daemon's --interpolated-path option
  git_connect: let user override virtual-host we send to daemon

connect.c

@@ -669,10 +669,20 @@ struct child_process *git_connect(int fd[2], const char *url,
 		printf("Diag: path=%s\n", path ? path : "NULL");
 		conn = NULL;
 	} else if (protocol == PROTO_GIT) {
+		/*
+		 * Set up virtual host information based on where we will
+		 * connect, unless the user has overridden us in
+		 * the environment.
+		 */
+		char *target_host = getenv("GIT_OVERRIDE_VIRTUAL_HOST");
+		if (target_host)
+			target_host = xstrdup(target_host);
+		else
+			target_host = xstrdup(hostandport);
+
 		/* These underlying connection commands die() if they
 		 * cannot connect.
 		 */
-		char *target_host = xstrdup(hostandport);
 		if (git_use_proxy(hostandport))
 			conn = git_proxy_connect(fd, hostandport);
 		else