Merge branch 'jk/name-decoration-alloc'

Merge branch 'jk/name-decoration-alloc'

The API to allocate the structure to keep track of commit
decoration was cumbersome to use, inviting lazy code to
overallocate memory.

* jk/name-decoration-alloc:
  log-tree: use FLEX_ARRAY in name_decoration
  log-tree: make name_decoration hash static
  log-tree: make add_name_decoration a public function