git pull is not robust.

Now I use `git rev-parse --abbrev-rev HEAD` to get the branch name, and
then `git reset --hard` to force the update to the last revision of the
branch.

Maintenance/infrastructure/cgal.geometryfactory.com/bin/create_release

@@ -5,7 +5,10 @@ export LC_ALL
 
 if [ -d "$1/.git" ]; then
     pushd $1
-    git pull
+    branch=`git rev-parse --abbrev-ref HEAD`
+    echo "Git repository, in branch '$branch'"
+    git fetch
+    git reset --hard origin/$branch
     popd
 else
     svn up "$1"