context: also accept diff option directly

For now we accept both diff option and dictionary. This will let us upgrade
internal users gradually before we drop the old API at the end of this series.

mercurial/context.py

@@ -30,6 +30,7 from . import (
     error,
     fileset,
     match as matchmod,
+    mdiff,
     obsolete as obsmod,
     patch,
     pathutil,
@@ -302,7 +303,11 class basectx(object):
             ctx2 = self.p1()
         if ctx2 is not None:
             ctx2 = self._repo[ctx2]
-        diffopts = patch.diffopts(self._repo.ui, opts)
+
+        if isinstance(opts, mdiff.diffopts):
+            diffopts = opts
+        else:
+            diffopts = patch.diffopts(self._repo.ui, opts)
         return patch.diff(self._repo, ctx2, self, match=match, changes=changes,
                           opts=diffopts, losedatafn=losedatafn, prefix=prefix,
                           relroot=relroot, copy=copy,