git tools: Make error messages more clear.

tools/reset-to-pull-request

@@ -4,7 +4,9 @@ set -x
 
 if ! git diff-index --quiet HEAD; then
     set +x
-    echo "There are uncommitted files. Exiting."
+    echo "There are uncommitted changes:"
+    git status --short
+    echo "Doing nothing to avoid losing your work."
     exit 1
 fi
 request_id="$1"