Add a .gitignore file for the downloaded testdata.

.gitignore

@@ -0,0 +1,11 @@
+testdata/alice29.txt
+testdata/asyoulik.txt
+testdata/fireworks.jpeg
+testdata/geo.protodata
+testdata/html
+testdata/html_x_4
+testdata/kppkn.gtb
+testdata/lcet10.txt
+testdata/paper-100k.pdf
+testdata/plrabn12.txt
+testdata/urls.10K

snappy_test.go

@@ -465,6 +465,9 @@ func BenchmarkRandomEncode(b *testing.B) {
 // testFiles' values are copied directly from
 // https://raw.githubusercontent.com/google/snappy/master/snappy_unittest.cc
 // The label field is unused in snappy-go.
+//
+// If this list changes (due to the upstream C++ list changing), remember to
+// update the .gitignore file in this repository.
 var testFiles = []struct {
 	label     string
 	filename  string