tkdiff

Notes on importing from sourceforge.

Improve git support. Derived from https://sourceforge.net/p/tkdiff/patches/27/

Set initial size of horizontal scrollbar. https://sourceforge.net/p/tkdiff/patches/14/

Fix sync between windows, untested. https://sourceforge.net/p/tkdiff/patches/28/

Fix combobox on MacOS, untested. https://sourceforge.net/p/tkdiff/patches/29/