largefiles: add copytostore() fstandin argument to replace readstandin() (API)

copyalltostore(), only one caller of copytostore(), already knows
standin file name of the target largefile. Therefore, passing it to
copytostore() is more efficient than calculating it in copytostore()
or readstandin().

hgext/largefiles/lfutil.py

@@ -245,9 +245,9 b' def copyfromcache(repo, hash, filename):'
         return False
     return True
 
-def copytostore(repo, revorctx, file, uploaded=False):
+def copytostore(repo, revorctx, file, fstandin, uploaded=False):
     wvfs = repo.wvfs
-    hash = readstandin(repo, file, revorctx)
+    hash = readasstandin(repo[revorctx][fstandin])
     if instore(repo, hash):
         return
     if wvfs.exists(file):
@@ -263,7 +263,7 b' def copyalltostore(repo, node):'
     for filename in ctx.files():
         realfile = splitstandin(filename)
         if realfile is not None and filename in ctx.manifest():
-            copytostore(repo, ctx, realfile)
+            copytostore(repo, ctx, realfile, filename)
 
 def copytostoreabsolute(repo, file, hash):
     if inusercache(repo.ui, hash):