Add unsymlinked.git test repository
diff: refactor git_diff_tree_to_tree() tests
diff: Enhance tree-to-tree diff test coverage

These tests are related to issue libgit2/libgit2sharp#196
Merge pull request #1318 from nulltoken/topic/diff-tree-coverage

Topic/diff tree coverage
push: fix typo in git_push_finish() doc
Merge pull request #1342 from ghedo/development

push: fix typo in git_push_finish() doc