This tests the fixes for issues from #1849

Treewalker

Prevent git_tree_walk 'skip entry' callback return code from leaking through as the return value of git_tree_walk

Fix cl_assert_equal_sz error message formating

SSH: Clone fails with errors: ERROR: Repository invalid & Early EOF

errors: Fix format of some error messages

revwalk: allow simplifying by first-parent

Make odb_loose return EAMBIGUOUS when required

When enabled, only the first parent of each commit will be queued,
enabling a simple way of using first-parent simplification.

fixing headers with bad values for objective-c

fixes issues with objective-git

odb: Error when streaming in less|more bytes than declared

Fix memory leaks

Some revparse love

revwalk: make mark_unintersting use a loop

Ask the odbbackend if the object exists before overwriting it

Now that #1785 is merged, git_odb_stream_finalize_write() calculates the object id before invoking the odb backend.

This commit gives a chance to the backend to check if it already knows this object.