Have buildVignette() remove build timestamp unless not cleaning up.

git-svn-id: https://svn.r-project.org/R/trunk@66862 00db46b3-68df-0310-9c12-caf00c1e9a41
Spelling.


git-svn-id: https://svn.r-project.org/R/trunk@66863 00db46b3-68df-0310-9c12-caf00c1e9a41