Before this patch, there were two code paths: either getting the only
the wanted content by calling git-archive, or cloning the repository and
copying the files.
Both these approaches have the downside of not allowing retriving
content from a specific git commit.
The workaround is to create a new empty repo (in the location to which
we cloned previously), fetching the specific commit to there and then
checking it out.
This supports any commit and works identically for any protocol. The
downside is that all files in that commit will be downloaded. It should
be no worse than the git-clone path, but can result in bigger transfers
than git-archive.
Unfortunately this is only supported with git 2.5+. On older version
fetch will fail with no error message (tested with 1.8.3). This can be
used to fall back to full clone. This fallback is clearly suboptimal in
terms of data transfer, but it should work reliably.
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>
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