ipython/ipython — pull request #1965 by ivanov (2012-06-15 01:28:57+00:00)
Title: fix for #1678, undo no longer clears cells

With these changes, `ctrl-z` inside of codemirror cells will only undo up to the text that was in the cell when it was loaded from JSON.

I found another bug where switching the cell type causes the loss of all
undo history for that cell. With this commit, switching the cell type
simply resets the history.