lfs: allow to run 'debugupgraderepo' on repo with largefiles

The extensions wrap the necessary function to ensure the 'lfs' requirements
won't be dropped.

It is now possible to run `hg debugupgraderepo` on a repository with lfs.

hgext/lfs/__init__.py

@@ -46,6 +46,7 from mercurial import (
     registrar,
     revlog,
     scmutil,
+    upgrade,
     vfs as vfsmod,
 )
 
@@ -139,6 +140,12 def extsetup(ui):
 
     wrapfunction(scmutil, 'wrapconvertsink', wrapper.convertsink)
 
+    wrapfunction(upgrade, 'preservedrequirements',
+                 wrapper.upgraderequirements)
+
+    wrapfunction(upgrade, 'supporteddestrequirements',
+                 wrapper.upgraderequirements)
+
     wrapfunction(changegroup,
                  'supportedoutgoingversions',
                  wrapper.supportedoutgoingversions)

hgext/lfs/wrapper.py

@@ -302,3 +302,9 def uploadblobs(repo, pointers):
 
     remoteblob = repo.svfs.lfsremoteblobstore
     remoteblob.writebatch(pointers, repo.svfs.lfslocalblobstore)
+
+def upgraderequirements(orig, repo):
+    reqs = orig(repo)
+    if 'lfs' in repo.requirements:
+        reqs.add('lfs')
+    return reqs