t: add a test for fetching from alternate repositories

Until recently, gitobj did not understand how to read from alternate
repositories.  This caused us to think objects not in the local
repository were missing, and consequently, to cause the object scanner
to exit early and a deadlock.  Since both of these issue are now fixed,
add a test that we can fetch from a shared repository without hangs or
failures.

Author: bk2204

t/t-fetch.sh

@@ -51,8 +51,9 @@ begin_test "init for fetch tests"
   git push origin newbranch
   assert_server_object "$reponame" "$b_oid"
 
-  # This clone is used for subsequent tests
+  # These clones are used for subsequent tests
   clone_repo "$reponame" clone
+  git clone --shared "$TRASHDIR/clone" "$TRASHDIR/shared"
 )
 end_test
 
@@ -70,6 +71,21 @@ begin_test "fetch"
 )
 end_test
 
+begin_test "fetch (shared repository)"
+(
+  set -e
+  cd shared
+  rm -rf .git/lfs/objects
+
+  git lfs fetch 2>&1 | tee fetch.log
+  ! grep "Could not scan" fetch.log
+  assert_local_object "$contents_oid" 1
+
+  git lfs fsck 2>&1 | tee fsck.log
+  grep "Git LFS fsck OK" fsck.log
+)
+end_test
+
 begin_test "fetch with remote"
 (
   set -e