don't say "install complete" when it really isn't

Change the recovery UI so that when there is a hboot or radio update
pending (which the user most do a home+back reboot to actually
install), the UI tells them so, instead of saying "Install from sdcard
complete."
diff --git a/firmware.c b/firmware.c
index 34b2918..e2e4fe6 100644
--- a/firmware.c
+++ b/firmware.c
@@ -39,6 +39,10 @@
     return 0;
 }
 
+// Return true if there is a firmware update pending.
+int firmware_update_pending() {
+  return update_data != NULL && update_length > 0;
+}
 
 /* Bootloader / Recovery Flow
  *