prepare_notebooks.sh now does not affecgt existing notebooks

setup_eth_euler/prepare_notebooks.sh

@@ -8,6 +8,21 @@
 
 set -e
 
+# we have inplace changes we don't want to spoil to # "real" branches.
+# we 1. determine current branch,
+# 2. setup error handler to switch back to previous branch in all casses
+# 3. create a new branch
+OLD_BRANCH=$(/usr/local/bin/git branch --show-current)
+WORK_BRANCH=setup_euler_temp_branch
+cleanup() {
+      echo CLEANUP
+      git checkout ${OLD_BRANCH}
+      git branch -D ${WORK_BRANCH}
+  }
+trap cleanup 0
+
+git checkout -b ${WORK_BRANCH}
+
 # files to include for installation:
 NOTEBOOKS=??_*.ipynb
 
@@ -47,4 +62,3 @@ done
 
 popd >/dev/null
 echo
-