The --reroll-count=$N option, when given a positive integer:
- Adds " v$N" to the subject prefix specified. As the default
subject prefix string is "PATCH", --reroll-count=2 makes it
"PATCH v2".
- Prefixes "v$N-" to the names used for output files. The cover
letter, whose name is usually 0000-cover-letter.patch, becomes
v2-0000-cover-letter.patch when given --reroll-count=2.
This allows users to use the same --output-directory for multiple
iterations of the same series, without letting the output for a
newer round overwrite output files from the earlier rounds. The
user can incorporate materials from earlier rounds to update the
newly minted iteration, and use "send-email v2-*.patch" to send out
the patches belonging to the second iteration easily.