Add functionality for inspecting check results/details changes.

git-svn-id: https://svn.r-project.org/R/trunk@66599 00db46b3-68df-0310-9c12-caf00c1e9a41
Consolidate and enhance.

git-svn-id: https://svn.r-project.org/R/trunk@66600 00db46b3-68df-0310-9c12-caf00c1e9a41
setCompilerOptions returns result invisibly and initioan optimizaiton
level can now be set with an environment variable.


git-svn-id: https://svn.r-project.org/R/trunk@66601 00db46b3-68df-0310-9c12-caf00c1e9a41