gnulib-tool.py: Make --extract-dependents quick again. Suggested by Bruno Haible in: <https://lists.gnu.org/archive/html/bug-gnulib/2024-12/msg00012.html>. * pygnulib/GLModuleSystem.py (GLModule.getDependents): Add an optional argument to use the implementation before yesterdays change. * pygnulib/main.py (mode == 'extract-dependents'): Add the optional argument to call of GLModule.getDependents.