gnulib-tool.py: Accept valid make syntax for escaped newlines. * pygnulib/GLModuleSystem.py (GLModuleTable.add_dummy): Use combine_lines instead of remove remove_backslash_newline so spaces are added between each combined line. * pygnulib/GLTestDir.py (GLTestDir.execute): Likewise. * pygnulib/constants.py (remove_backslash_newline): Remove unused function.