Following commit 95a572282e (pkg-infra: move the git download helper to a
script, 2014-07-02), move the comment describing the shallow clone trickery as
well. Merge this comment with the existing helper comment that was added in
7e40a1103a (support/download: convert git to use the wrapper, 2014-08-03).
Rename $($(PKG)_DL_VERSION) to ${cset} to match the helper code context.
Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>