gnulib-tool: Improve changes from yesterday and today. * gnulib-tool.sh (func_emit_tests_Makefile_am): Consider also the case that --with-tests is specified and --makefile-name / --tests-makefile-name are not specified. Simplify an initialization and augmentation to an initialization. * pygnulib/GLEmiter.py (GLEmiter.tests_Makefile_am): Likewise.