largefiles: fix an explicit largefile commit after a remove (issue4969)

The change in b68797f244e4 to handle a normal -> largefile switch was too
aggressive in preserving the original matcher names.  If a largefile is
explicitly provided by the user, but only the standin exists in dirstate, then
only the standin can be committed.

There's still maybe an issue when the largefile is deleted outside of Mercurial:

  $ rm large
  $ hg ci -m "oops" large
  large: The system cannot find the file specified
  nothing changed
  [1]

hgext/largefiles/lfutil.py

@@ -575,11 +575,15 b' def updatestandinsbymatch(repo, match):'
         fstandin = standin(f)
 
         # For largefiles, only one of the normal and standin should be
-        # committed (except if one of them is a remove).
+        # committed (except if one of them is a remove).  In the case of a
+        # standin removal, drop the normal file if it is unknown to dirstate.
         # Thus, skip plain largefile names but keep the standin.
-        if (f in lfiles or fstandin in standins) and \
-            repo.dirstate[f] != 'r' and repo.dirstate[fstandin] != 'r':
-            continue
+        if f in lfiles or fstandin in standins:
+            if repo.dirstate[fstandin] != 'r':
+                if repo.dirstate[f] != 'r':
+                    continue
+            elif repo.dirstate[f] == '?':
+                continue
 
         actualfiles.append(f)
     match._files = actualfiles

tests/test-largefiles-cache.t

@@ -17,7 +17,7 b' Create source repo, and commit adding la'
   $ hg add --large large
   $ hg commit -m 'add largefile'
   $ hg rm large
-  $ hg commit -m 'branchhead without largefile'
+  $ hg commit -m 'branchhead without largefile' large
   $ hg up -qr 0
   $ cd ..