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