existing contents of `.git/FETCH_HEAD`. Without this
option old data in `.git/FETCH_HEAD` will be overwritten.
---upload-pack <upload-pack>::
--u <upload-pack>::
+\--upload-pack <upload-pack>::
When given, and the repository to fetch from is handled
by 'git-fetch-pack', '--exec=<upload-pack>' is passed to
the command to specify non-default path for the command