fix bug: restarting R after closing a project applies project state

RStudio saves the last project opened, so it can be restored when the
IDE boots up (if the user has "Restore most recently opened project"
set in their UI prefs). When a project is closed, this setting's value
can persist, and when the R session is coming back after a restart, the
value is applied, putting some parts of the IDE into project state
while others remain outside project state.
Merge pull request #137 from rstudio/bugfix/project-restart

fix bug: restarting R after closing a project applies project state