commands.summary: switch to mergestate.read()

See previous patch for why we're doing this.

We do this with a bit of care -- it would be bad form for 'hg summary' to abort
completely if we encounter an unsupported merge record. Instead just warn about
that and continue with the rest of the summary.

mercurial/commands.py

@@ -6208,8 +6208,15 b' def summary(ui, repo, **opts):'
         if d in status.added:
             status.added.remove(d)
 
-    ms = mergemod.mergestate(repo)
-    unresolved = [f for f in ms if ms[f] == 'u']
+    try:
+        ms = mergemod.mergestate.read(repo)
+    except error.UnsupportedMergeRecords as e:
+        s = ' '.join(e.recordtypes)
+        ui.warn(
+            _('warning: merge state has unsupported record types: %s\n') % s)
+        unresolved = 0
+    else:
+        unresolved = [f for f in ms if ms[f] == 'u']
 
     subs = [s for s in ctx.substate if ctx.sub(s).dirty()]