Merge branch 'rs/unpack-trees-plug-leak'

* rs/unpack-trees-plug-leak:
  unpack-trees: free cache_entry array members for merges
  diff-lib, read-tree, unpack-trees: mark cache_entry array paramters const
  diff-lib, read-tree, unpack-trees: mark cache_entry pointers const
  unpack-trees: create working copy of merge entry in merged_entry
  unpack-trees: factor out dup_entry
  read-cache: mark cache_entry pointers const
  cache: mark cache_entry pointers const

diff --cc cache.h
Simple merge