Squashed 'deps/libgit2/' changes from 64dc248..057126c

057126c Merge pull request #2637 from libgit2/cmn/global-init
799e22e Rename git_threads_ to git_libgit2_
4865cc3 Merge pull request #2673 from swisspol/2672
e284c45 Changed GIT_REMOTE_DOWNLOAD_TAGS_ALL to behave like git 1.9.0
02bc523 Merge pull request #2698 from libgit2/cmn/fetchhead-refactor
bc8c4a8 Merge pull request #2695 from libgit2/cmn/remote-lookup
e3bd48a Merge pull request #2696 from libgit2/cmn/empty-objects
09d1408 Merge pull request #2694 from Therzok/statusFile
2c9b9c8 remote: refactor the reference-update decision
e1ac010 odb: hardcode the empty blob and tree
64fdd86 remote: don't check for upstream on an anonymous remote
e235db0 remote: use git_branch_upstream_remote()
82374d9 branch: add getter for the upstream remote name
209425c remote: rename _load() to _lookup()
6818208 git_status_file now takes an exact path
4e1b3b3 Merge pull request #2691 from libgit2/cmn/submodule-and-dir
62a617d iterator: submodules are determined by an index or tree
f1a7906 submodules: add failing test for stale module entries
dd83e60 Merge pull request #2692 from ethomson/bug2515
2d24816 checkout_index: Remove stage 0 when checking out conflicts
9f66434 checkout_index: remove conflicts when checking out new files

git-subtree-dir: deps/libgit2
git-subtree-split: 057126c6d3b49c0c87dbc0c02e6b551792836e7b
Merge commit 'df7208b1f3c686214830a913d540e3f7e65e8acc' into jacquesg/update-libgit2
Raw.xs: git_threads_init() has been renamed to git_libgit2_init()
Remote.xs: git_remote_load() has been renamed to git_remote_lookup()
Changes: update