Consolidate notion of (package) vignette.

git-svn-id: https://svn.r-project.org/R/trunk@63466 00db46b3-68df-0310-9c12-caf00c1e9a41
Support two-stage install/check in .check_make_vars().

git-svn-id: https://svn.r-project.org/R/trunk@63467 00db46b3-68df-0310-9c12-caf00c1e9a41