tests: add subrepo recursion tests for add/forget with explicit paths

When support for handling add/forget of explicit paths within subrepos was
added (9e99d2bbb1b1/95174c381525), nested subrepos weren't handled properly.
This change adds test coverage to expose the broken behavior, which will be
fixed in later patches.

tests/test-subrepo-recursion.t

@@ -188,6 +188,30 b' Cleanup and final commit:'
   committing subrepository foo
   committing subrepository foo/bar (glob)
 
+Test explicit path commands within subrepos: add/forget
+  $ echo z1 > foo/bar/z2.txt
+  $ hg status -S
+  ? foo/bar/z2.txt
+  $ hg add foo/bar/z2.txt
+This is expected to add the file, but is currently broken
+  $ hg status -S
+  ? foo/bar/z2.txt
+When fixed, remove the next two commands
+  $ hg add -R foo/bar foo/bar/z2.txt
+  $ hg status -S
+  A foo/bar/z2.txt
+This is expected to forget the file, but is currently broken
+  $ hg forget foo/bar/z2.txt
+  not removing foo/bar/z2.txt: file is already untracked
+  [1]
+  $ hg status -S
+  A foo/bar/z2.txt
+When fixed, remove the next two commands
+  $ hg forget -R foo/bar foo/bar/z2.txt
+  $ hg status -S
+  ? foo/bar/z2.txt
+  $ rm foo/bar/z2.txt
+
 Log with the relationships between repo and its subrepo:
 
   $ hg log --template '{rev}:{node|short} {desc}\n'