Controlled R Sessions for Each Widget

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Code enhancement.

One code enhancement that may be explored will be to allow each widget to 
control a separate R environment or subset of variables.  These could be 
individually saved and reloaded as needed.  For example once a dataset is 
subset the orriginal dataset can be saved to the tempdir and the subset can be 
worked on allowing a relative expansion of available memory.

This would involve some changes to the signals and RSession.  Session calls may 
require some extra variable names to ensure that those variables are active in 
the session.  This could be checked quickly in R.

The use of the QTimer class could be implemented to "close" or "dump" R 
variables to disk to free memory automatically.

A branch will be made to explore this issue.

Original issue reported on code.google.com by kylecovi...@gmail.com on 30 Jan 2011 at 8:22