largefiles: replace match.bad() monkey patching with match.badmatch()

No known issues with the previous code since it restored the original method,
but this is cleaner.

The monkey patching in cat is harmless, because it is created locally, and
doesn't pass it anywhere (subrepo cat isn't supported with largefiles).

hgext/largefiles/overrides.py

@@ -100,10 +100,10 b' def addlargefiles(ui, repo, isaddremove,'
             lfmatcher = match_.match(repo.root, '', list(lfpats))
 
     lfnames = []
-    m = copy.copy(matcher)
-    m.bad = lambda x, y: None
+    m = matcher
+
     wctx = repo[None]
-    for f in repo.walk(m):
+    for f in repo.walk(match_.badmatch(m, lambda x, y: None)):
         exact = m.exact(f)
         lfile = lfutil.standin(f) in wctx
         nfile = f in wctx