Allow package trees (packages with subpackages) to share common distributed auxiliary files (and directories) that reside within a subpackage. * lib/am/distdir.am (distdir %?TOPDIR_P%): Do not fail if `$(distdir)' already exists. (%?SUBDIRS%): Set `am__remove_distdir' to `:' to prevent removal of subpackage trees for distribution. * tests/subpkg3.test: New test. * tests/Makefile.am: Update.