subr/pkg_{autoconf,configure,patch}.subr: reference ${PKG_BASE_DIR} instead of ${WORKDIR}.
    subr/pkg_build_dir.subr: {build,install} packages nested within ${PKG_BUILD_DIR}/.
    subr/pkg_distclean.subr: removed from repository.
    subr/pkg_{extract,fetch}.subr: {extract,fetch} within ${PKG_BASE_DIR}.
    subr/pkg_install.subr: install to ../destdir to facilitate post-installation processing.
    subr/pkg_setup_env.subr: set & create ${PKG_BASE_DIR}.
    subr/pre_subdirs.subr: always create ${PREFIX}/bin.
    vars/build.vars: consistently use ${PKG_{PREFIX,MAKE_INSTALL_VNAME,MAKEFLAGS_INSTALL}}.
    vars/env.vars, *: cleanup.