Repository#include?: support short SHA1s
Add methods to make using Rugged::Diff#stat more user friendly.
Remove `Rugged::Diff#tree` and `Rugged::Diff#owner`.

Fixes #389.
Merge pull request #392 from libgit2/arthur/remove-diff-owner

Remove `Rugged::Diff#tree` and `Rugged::Diff#owner`.
Remove defunct `Rugged::Diff::Line#hunk` and `Rugged::Diff::Line#owner`.

Fixes #390.
Merge pull request #393 from libgit2/arthur/remove-diff-line-owner

Remove defunct `Rugged::Diff::Line#hunk` and `Rugged::Diff::Line#owner`.
Add rb_git_remote_check_connection

This is useful if one needs to check if it is possible to
fetch/push from/to the remote.

Basically this is the analogue to `git fetch --dry-run` and `git push
--dry-run`.
Merge pull request #397 from dmedvinsky/remote-check-connection

Add rb_git_remote_check_connection
Bump libgit2 to 9de6ec52008e3f30a4e8a5c6a13859eefcf86f57