Make update-version script more usable.

- Fail if uncommited or staged changes are in the working directory.
- Show the version changes as a diff.
- On success show the commit log message.

packaging/update-version

@@ -4,9 +4,12 @@
 set -e
 
 
-# Script only runs at the codebase root.
+# Only run at the codebase root.
 [ $(basename $PWD) == "eris" ]
 [ -e README.md ]
+# Don't run with uncommited or staged changes.
+git diff --exit-code
+git diff --cached --exit-code
 
 
 NEW_VERSION=$(date "+v%Y.%m.%d")
@@ -15,6 +18,8 @@ if [ $NEW_VERSION == $CURRENT_VERSION ]; then
     git tag --delete $CURRENT_VERSION
 else
     git grep -l $CURRENT_VERSION | xargs sed -i "s/$CURRENT_VERSION/$NEW_VERSION/g"
+    git diff
     git commit --all --message="Update version from $CURRENT_VERSION to $NEW_VERSION."
 fi
 git tag $NEW_VERSION
+git log --max-count=1