git-lfs: fixed tests for upload, and added new for file verification.

git-lfs: make usage of gunicorn wrappers to write data to disk. - instead of turning it into a seekable object we write the data directly from gunicorn Body object. This has consistent behaviour on chunked vs non chunked data.

git-lfs: report chunked encoding support properly to the client. - this allows streaming support of ANY binaries.

git-lfs: report returned data as 'application/vnd.git-lfs+json' instead of plain json

git-lfs: always validate uploaded files size. In case of bad uploads we want the client to re-try the LFS object upload. Else we can end up with wrong sized OIDs uploaded and reported as OK.

release: merge back stable branch into default

Added tag v4.7.1 for changeset 57f527e0646d

release: Finish preparation for 4.7.1

release: updated pip2nix output for 4.7.1

release: Start preparation for 4.7.1