[GSoC][PATCH v4 3/4] submodule: port set_name_rev() from shell to C

LGTM with nits

commit message:

"revision name, and later handles its formating and printing."

typo: formatting

+ if (!capture_command(&cp, &sb, 0) && sb.len) { + strbuf_strip_suffix(&sb, "\n"); + return strbuf_detach(&sb, NULL); + }

you discard all output if these commands fail, so if the argument is a not a submodule, or the other is not a sha1, it will just print nothing without error message. Maybe that is OK, though? I don't see documentation for these commands, so maybe this is not meant to be usable?