vheaders can be used when not defined

git-svn-id: https://svn.r-project.org/R/trunk@62666 00db46b3-68df-0310-9c12-caf00c1e9a41
is.unsorted(): follow doc:  length(x) == 1  is always sorted

git-svn-id: https://svn.r-project.org/R/trunk@62668 00db46b3-68df-0310-9c12-caf00c1e9a41
PR#15288 fix:  summaryRprof only read the first chunk of profile data when line.profiling was active.

git-svn-id: https://svn.r-project.org/R/trunk@62669 00db46b3-68df-0310-9c12-caf00c1e9a41