Merge branch 'jc/no-default-attr-tree-in-bare'

Merge branch 'jc/no-default-attr-tree-in-bare'

Git 2.43 started using the tree of HEAD as the source of attributes
in a bare repository, which has severe performance implications.
For now, revert the change, without ripping out a more explicit
support for the attr.tree configuration variable.

* jc/no-default-attr-tree-in-bare:
  stop using HEAD for attributes in bare repository by default