largefiles: remove a mutable default argument

Mutable default arguments are know to the state of California to cause bugs.

hgext/largefiles/overrides.py

@@ -50,8 +50,10 b' def composenormalfilematcher(match, mani'
 
 def installnormalfilesmatchfn(manifest):
     '''installmatchfn with a matchfn that ignores all largefiles'''
-    def overridematch(ctx, pats=(), opts={}, globbed=False,
+    def overridematch(ctx, pats=(), opts=None, globbed=False,
             default='relpath', badfn=None):
+        if opts is None:
+            opts = {}
         match = oldmatch(ctx, pats, opts, globbed, default, badfn=badfn)
         return composenormalfilematcher(match, manifest)
     oldmatch = installmatchfn(overridematch)