submodule.c: report the submodule that an error occurs in
When an error occurs in updating the working tree of a submodule in
submodule_move_head, tell the user which submodule the error occurred in.
The call to read-tree contains a super-prefix, such that the read-tree
will correctly report any path related issues, but some error messages
do not contain a path, for example:
~/gerrit$ git checkout --recurse-submodules origin/master
~/gerrit$ fatal: failed to unpack tree object
07672f31880ba80300b38492df9d0acfcd6ee00a
Give the hint which submodule has a problem.
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>