forked children should not use exit

git-svn-id: https://svn.r-project.org/R/trunk@66457 00db46b3-68df-0310-9c12-caf00c1e9a41
tweaks

git-svn-id: https://svn.r-project.org/R/trunk@66459 00db46b3-68df-0310-9c12-caf00c1e9a41
more care with specifications of numbers of cores

git-svn-id: https://svn.r-project.org/R/trunk@66460 00db46b3-68df-0310-9c12-caf00c1e9a41
Port c66302 to R-patched.

git-svn-id: https://svn.r-project.org/R/trunk@66462 00db46b3-68df-0310-9c12-caf00c1e9a41
Write out 'DONE' after completing checking.

git-svn-id: https://svn.r-project.org/R/trunk@66465 00db46b3-68df-0310-9c12-caf00c1e9a41
Add travis builds