#8 split window mode with optional locked scrolling

[Anonymous]

A split window mode is often useful for comparing changes
between two files. I do like the tab MDI mode that is now
the default in 0.2.6, but it would be nice to be able to have
two files displayed at once (with left/right and top/bottom
splits). An icon to select locking of the scrollbars so that the
windows scroll together would be a useful feature too.

This will also be useful later, if somebody decides to
implement a python extension to highlight the differences
between the two files.