Add a test for search links in module aliases

Signed-off-by: Paul-Elliot <peada@free.fr>

Author: panglesd

test/search/module_aliases.t/main.ml

@@ -0,0 +1,5 @@
+module X = struct
+  let x = 1
+end
+
+module Y = X

test/search/module_aliases.t/run.t

@@ -0,0 +1,19 @@
+Compile the files
+
+  $ ocamlc -c main.ml -bin-annot -I .
+
+Compile and link the documentation
+
+  $ odoc compile main.cmt
+  $ odoc link main.odoc
+  $ odoc compile-index main.odocl
+
+We have a problem: The ID for Y generates an URL to a file which is not
+generated (as the module does not have an expansion).
+
+  $ cat index.json | jq | grep url |grep Y
+        "url": "Main/Y/index.html",
+
+  $ odoc html-generate -o html main.odocl && ls Main/Y/index.html
+  ls: cannot access 'Main/Y/index.html': No such file or directory
+  [2]