Add test for footnote references in doc summary

tests/rustdoc/footnote-in-summary.rs

@@ -0,0 +1,17 @@
+// This test ensures that no footnote reference is generated inside
+// summary doc.
+
+#![crate_name = "foo"]
+
+// @has 'foo/index.html'
+// @has - '//*[@class="desc docblock-short"]' 'hello bla'
+// @!has - '//*[@class="desc docblock-short"]/sup' '1'
+
+// @has 'foo/struct.S.html'
+// @has - '//*[@class="docblock"]//sup' '1'
+// @has - '//*[@class="docblock"]' 'hello 1 bla'
+
+/// hello [^foot] bla
+///
+/// [^foot]: blabla
+pub struct S;