lo-commit-stat: allow to list commits between branches
lo-commit-stat: allow to list commits between branches

use "git rev-list --pretty=medium" instead of "git log"
to be able to use origin/libreoffice-3-4 ^origin/libreoffice-3-3
to generate list of changes that are in 3.4 but not in 3.3

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core