Finish the conditional dependencies mechanism. * gnulib-tool: New option --no-conditional-dependencies. (func_usage): Document it. Don't mark --conditional-dependencies as experimental. (cond_dependencies): The possible values can now be true, false, empty. (func_modules_transitive_closure, func_emit_autoconf_snippets): Update. (func_import): Store setting in gnulib-cache.m4 and read it from there. * doc/gnulib-tool.texi (Conditional dependencies): New section.