Added one-tree constructor to DirCacheCheckout

When DirCacheCheckout should be used to checkout only one
tree (reset --hard, clone) then we had to use the standard
constructor and specify null as value for head. This change
adds explicit constructors not taking HEAD and documents
that.

Bug: 330021
Signed-off-by: Christian Halstrick <christian.halstrick@sap.com>
1 file changed