lfs: add the '{oid}' template keyword to '{lfs_files}'

The 'sha256:' prefix is skipped because this seems like the most convenient way
to consume it.  Maybe we should also add a '{oid_type}' keyword?  Then again,
that can be added in the future if a different algorithm is supported.

hgext/lfs/__init__.py

@@ -230,6 +230,7 b' def lfsfiles(repo, ctx, **args):'
 
     makemap = lambda v: {
         'file': v,
+        'oid': pointers[v].oid(),
     }
 
     # TODO: make the separator ', '?

tests/test-lfs.t

@@ -859,10 +859,11 b" there's no 'lfs' destination repo requir"
   oid sha256:5bb8341bee63b3649f222b2215bde37322bea075a30575aa685d8f8d21c77024
   size 29
   x-is-binary 0
-  $ hg --cwd convert_lfs log -r 'all()' -T '{rev}: {lfs_files % "{file}\n"}'
-  0: a1
-  1: a2
-  2: a2
+  $ hg --cwd convert_lfs \
+  >     log -r 'all()' -T '{rev}: {lfs_files % "{file}: {oid}\n"}'
+  0: a1: 5bb8341bee63b3649f222b2215bde37322bea075a30575aa685d8f8d21c77024
+  1: a2: 5bb8341bee63b3649f222b2215bde37322bea075a30575aa685d8f8d21c77024
+  2: a2: 876dadc86a8542f9798048f2c47f51dbf8e4359aed883e8ec80c5db825f0d943
 
   $ grep 'lfs' convert_lfs/.hg/requires
   lfs