In v2.9.0, we prematurely flipped the default to force cloning
submodules shallowly, when the superproject is getting cloned
shallowly. This is likely to fail when the upstream repositories
submodules are cloned from a repository that is not prepared to
serve histories that ends at a commit that is not at the tip of a
branch, and we know the world is not yet ready.
Use a safer default to clone the submodules fully, unless the user
tells us that she knows that the upstream repository of the
submodules are willing to cooperate with "--shallow-submodules"
option.
Noticed-by: Vadim Eisenberg <VADIME@il.ibm.com> Helped-by: Jeff King <peff@peff.net> Helped-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>