gnulib-tool.py: Refactor --makefile-name option. * gnulib-tool.py (main): Rename variable 'makefile' to 'makefile_name'. * pygnulib/GLConfig.py: Rename attribute 'makefile' to 'makefile_name'. * pygnulib/GLMakefileTable.py: Update. * pygnulib/GLEmiter.py: Likewise. * pygnulib/GLImport.py: Likewise. * pygnulib/GLFileSystem.py (GLFileAssistant): Remove unused assignment.