build: prevent empty directory in git checkout

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_3_1@1133159 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/solr/example/work/.gitignore b/solr/example/work/.gitignore
new file mode 100644
index 0000000..72e8ffc
--- /dev/null
+++ b/solr/example/work/.gitignore
@@ -0,0 +1 @@
+*