largefiles: test coverage of explicit commit of normal/largefile switch

This reveals that a switch from normal to largefile violates the normal
largefile invariant and gives a manifest with both a normal and standin file
in the repository, while a switch from largefile to normal gives nothing.
Not good.

tests/test-largefiles.t

@@ -1832,6 +1832,27 b' Test --normal flag'
   $ hg add --normal new-largefile
   new-largefile: up to 69 MB of RAM may be required to manage this file
   (use 'hg revert new-largefile' to cancel the pending addition)
+
+Test explicit commit of switch between normal and largefile - make sure both
+the add and the remove is committed.
+
+  $ hg up -qC
+  $ hg forget normal3 large4-renamed
+  $ hg add --large normal3
+  $ hg add large4-renamed
+  $ hg commit -m 'swap' normal3 large4-renamed
+  Invoking status precommit hook
+  A large4-renamed
+  A normal3
+  ? new-largefile
+  ? sub2/large6-renamed
+  $ hg mani
+  .hglf/normal3
+  .hglf/sub2/large6
+  .hglf/sub2/large7
+  normal3
+  sub/normal4
+
   $ cd ..