lfs: move the 'supportedoutgoingversions' handling to changegroup.py

This handling already exists here for the narrow extension.  We still need to
either figure out how to enable changegroup v3 without the extension, or figure
out how to let the server detect that the client doesn't have it loaded, and
emit a user friendly error[1].  I can't tell if D1944 is the appropriate vehicle
for the latter.

[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2018-January/109550.html

hgext/lfs/__init__.py

@@ -307,9 +307,6 b' def extsetup(ui):'
                  wrapper.upgraderequirements)
 
     wrapfunction(changegroup,
-                 'supportedoutgoingversions',
-                 wrapper.supportedoutgoingversions)
-    wrapfunction(changegroup,
                  'allsupportedversions',
                  wrapper.allsupportedversions)
 

hgext/lfs/wrapper.py

@@ -30,14 +30,6 b' from . import ('
     pointer,
 )
 
-def supportedoutgoingversions(orig, repo):
-    versions = orig(repo)
-    if 'lfs' in repo.requirements:
-        versions.discard('01')
-        versions.discard('02')
-    versions.add('03')
-    return versions
-
 def allsupportedversions(orig, ui):
     versions = orig(ui)
     versions.add('03')

mercurial/changegroup.py

@@ -36,6 +36,8 b' from .utils import ('
 _CHANGEGROUPV2_DELTA_HEADER = "20s20s20s20s20s"
 _CHANGEGROUPV3_DELTA_HEADER = ">20s20s20s20s20sH"
 
+LFS_REQUIREMENT = 'lfs'
+
 # When narrowing is finalized and no longer subject to format changes,
 # we should move this to just "narrow" or similar.
 NARROW_REQUIREMENT = 'narrowhg-experimental'
@@ -912,6 +914,12 b' def supportedoutgoingversions(repo):'
         # support that for stripping and unbundling to work.
         versions.discard('01')
         versions.discard('02')
+    if LFS_REQUIREMENT in repo.requirements:
+        # Versions 01 and 02 don't support revlog flags, and we need to
+        # mark LFS entries with REVIDX_EXTSTORED.
+        versions.discard('01')
+        versions.discard('02')
+
     return versions
 
 def localversion(repo):