ess-describe-object-at-point: show buffer first (useful for heavy objects)

git-svn-id: https://svn.r-project.org/ESS/trunk@5388 0bbaf3bd-34e0-0310-bf65-c717079852d4
ess-describe-object-at-point: if region is active, use it instead of the symbol at point

git-svn-id: https://svn.r-project.org/ESS/trunk@5389 0bbaf3bd-34e0-0310-bf65-c717079852d4