lfs: improve the error message for a missing remote blob

It seems better to print the name known to the user, not the internal file.  The
previous code unconditionally set 'p.filename'.  That potentially made the
attribute None, and would be printed as such in
_gitlfsremote._checkforservererror() instead of "unknown".  Normally, files are
printed relative to CWD, but I don't see a way to get the repo path to make that
adjustment.

The test modified here apparently only runs within Facebook, but a print
statement confirmed the name change.  I tried uploading the blob to a different
remote store (so the git server never saw it), and also killing the git server
and removing the blob directory, and removing the 'lfs.db' file.  All resulted
in a message:

  abort: LFS server claims required objects do not exist:
  bdc26931acfb734b142a8d675f205becf27560dc461f501822de13274fe6fc8a!

So I have no idea how to make this test generally runnable.

hgext/lfs/blobstore.py

@@ -240,7 +240,7 b' class _gitlfsremote(object):'
                     filename = getattr(p, 'filename', 'unknown')
                     raise LfsRemoteError(
                         _(('LFS server error. Remote object '
-                          'for file %s not found: %r')) % (filename, response))
+                          'for "%s" not found: %r')) % (filename, response))
                 raise LfsRemoteError(_('LFS server error: %r') % response)
 
     def _extractobjects(self, response, pointers, action):

hgext/lfs/wrapper.py

@@ -60,7 +60,7 b' def readfromstore(self, text):'
     oid = p.oid()
     store = self.opener.lfslocalblobstore
     if not store.has(oid):
-        p.filename = getattr(self, 'indexfile', None)
+        p.filename = self.filename
         self.opener.lfsremoteblobstore.readbatch([p], store)
 
     # The caller will validate the content

tests/test-lfs-test-server.t

@@ -185,7 +185,7 b' Check error message when object does not'
   $ rm -rf `hg config lfs.usercache`
   $ hg --config 'lfs.url=https://dewey-lfs.vip.facebook.com/lfs' clone test test2
   updating to branch default
-  abort: LFS server error. Remote object for file data/a.i not found:(.*)! (re)
+  abort: LFS server error. Remote object for "a" not found:(.*)! (re)
   [255]
 
   $ $PYTHON $RUNTESTDIR/killdaemons.py $DAEMON_PIDS