[PATCH 0/7] unpack-trees: plug memory leak for merges

This series adds const to cache_entry pointers in a lot of places, in
order to show that we can free them in unpack_nondirectories, which
the last patch finally does.

First three easy patches for adding const and splitting a function in
two:

  cache: mark cache_entry pointers const
  read-cache: mark cache_entry pointers const
  unpack-trees: factor out dup_entry

Then a patch that reduces the side effects of merged_entry:

  unpack-trees: create working copy of merge entry in merged_entry

Another easy const patch:

  diff-lib, read-tree, unpack-trees: mark cache_entry pointers const

And patch that introduces "const struct cache_entry * const *", which
may look a bit scary at first:

  diff-lib, read-tree, unpack-trees: mark cache_entry array paramters const

Final patch that plugs a memory leak in unpack_nondirectories.

  unpack-trees: free cache_entry array members for merges

It's basically the same one that Stephen tested a while ago
(http://thread.gmane.org/gmane.comp.version-control.git/222887).

It's not the only leak that affects cherry-pick; expect more
(independent) patches.

 builtin/read-tree.c |   5 +-
 cache.h             |  10 ++--
 diff-lib.c          |  26 +++++-----
 read-cache.c        |  18 ++++---
 unpack-trees.c      | 146 ++++++++++++++++++++++++++++++++--------------------
 unpack-trees.h      |  14 +++--
 6 files changed, 131 insertions(+), 88 deletions 
1.8.3