Issue233: Fold actions count as changes to a document

From #233

Since part of wxMaxima's functionality is to edit math documents, and the state of the folds in the document are saved in wxMaxima documents, it makes sense to count changes to the folds as changes for purpose of marking the file as unsaved (and thus allowing the user to save those changes easily with Ctrl+S).

This patch changes the behavior of folds so that they will mark the document as unsaved, thus allowing a user to easily save changes to the folding of groups without having to first evaluate an expression to cause the document to register as unsaved.

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Test file: https://dl.dropbox.com/u/11334386/wxmaxima/issue233.wxmx

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Also includes updates to doxygen comments and copyright year.