qview.xml: Fixed prompts for saving edited files on closing so they are...

qview.xml: Fixed prompts for saving edited files on closing so they are functional once again. Fixes #854. 
EditTool.h: 2012-05-24 Steven Lambright - Minor changes to support prompting to save on exit once again (this has been broken for a very long time). The prompt now appears if you have edited your file but not saved it - not when clicking "Save." This was a minimal fix (I left a lot of problems to be solved at a later date). Fixes #854. 
ViewportMdiSubWindow.h: 2012-05-29 Steven Lambright - Original implementation 
Workspace.h: 2012-05-29 Steven Lambright - Now utilizes ViewportMdiSubWindow instead of QMdiSubWindow. References #854. 
CubeViewport.h: 2012-05-29 Steven Lambright - Changed destructor to clean up the cube when necessary. 
MainWindow.h: 2012-05-29 Steven Lambright - Fixed a bug where closeEvent method was not calling the paren't version. 
ViewportMainWindow.h: 2012-05-29 Steven Lambright - Updated closeEvent() to ask the user to save any unsaved modifications to the opened cube. References #854. 
FileTool.h: 2012-05-24 Steven Lambright - Minor changes to support prompting to save on exit once again (this has been broken for a very long time). The prompt now appears if you have edited your file but not saved it - not when clicking "Save." This was a minimal fix (I left a lot of problems to be solved at a later date). Fixes #854. 

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4444 41f8697f-d340-4b68-9986-7bafba869bb8