re-fixing 5392 and C-c C-z problem in script buffer.

git-svn-id: https://svn.r-project.org/ESS/trunk@5394 0bbaf3bd-34e0-0310-bf65-c717079852d4
fixing the C-c C-z bug causing split of the frame even when the script buffer is present in other frame

git-svn-id: https://svn.r-project.org/ESS/trunk@5395 0bbaf3bd-34e0-0310-bf65-c717079852d4