Basically the same as the asterisk HOWTO.
Changes:
Initial clone is:
git svn clone -s http://svn.digium.com/svn/libpri
The .gitignore file is:
cp ../asterisk-tools/libpri_gitignore .gitignore
Libpri has no 'trunk' . So the master branch should follow 1.4:
git branch -D master
git branch --track -b master 1.4