OSTree v2015.6

[Colin Walters <walters verbum org>]

I promised more frequent releases, here's living up to that!

OSTree v2015.6 is now available via this GPG signed git commit:

https://git.gnome.org/browse/ostree/tag/?id=v2015.6

(Side note, I tweaked https://github.com/cgwalters/homegit/blob/master/bin/git-evtag to include the git 
version based on some discussion on the upstream git mailing list)

This release primarily adds:
 - Visible status from GPG (mbarnes)
 - Some new APIs necessary for rpm-ostree (walters)
 - A new repository option to automatically update the summary file (gscrivano)
 - Consistently honor the repository fsync policy (walters, gscrivano)
 - `ostree reset` no longer enforces parentage, which makes it more generally usable like git's (walters)

Colin Walters (8):
      pull-metalink: Don't print error output when we expect failure
      Add an API to set/unset a deployment tree's mutability
      refs: Use *at for writes, honor repo fsync flag
      repo: Add a private helper to replace a file, honoring fsync policy
      libglnx: Update to latest
      reset: Don't enforce parent commits
      sysroot: Add ostree_sysroot_get_fd()
      Release 2015.6

Giuseppe Scrivano (4):
      ostree_repo_checkout_tree_at: remove @subpath documentation
      _ostree_repo_file_replace_contents: make buf const
      summary: write the contents to a temporary file
      config: add new parameter "commit-update-summary" to core section

Matthew Barnes (11):
      gpg: Add ostree_gpg_verify_result_describe()
      admin: Show GPG signatures in status command
      libglnx: Pick up file permission regression fix
      tests: Fix root uid check in test-commit-sign.sh
      repo: Improve error handling in sign_data()
      repo: Add a "gpg-verify-result" signal
      pull: Print GPG signature status as soon as its known
      repo: Add ostree_repo_remote_get_gpg_verify()
      admin: Conditionally show GPG signatures in status command
      sysroot: Cache an OstreeRepo instance
      main: Tweak GPG output to match rpm-ostree