gnulib-tool.py: Fix --extract-dependencies result. * pygnulib/GLModuleSystem.py (GLModule.getDependencies): Return a snippet, not a list. Implement dependency of ${module}-tests on ${module}. (GLModule.getDependenciesWithoutConditions, GLModule.getDependenciesWithConditions): New methods. (GLModuleTable.transitive_closure): Call getDependenciesWithConditions. * pygnulib/GLEmiter.py (GLEmiter.autoconfSnippets): Call getDependenciesWithoutConditions. * gnulib-tool.py (main) [--extract-dependencies]: Update.