When diff drivers are installed, calling "git diff <tree1>..<tree2>"
calls those drivers. This borks the patch generation of rebase -i.
So use "git diff-tree -p" instead, which does not call diff drivers.
Noticed by Johannes Sixt.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Lars Hjemli <hjemli@gmail.com> Signed-off-by: Shawn O. Pearce <spearce@spearce.org>