The keyword specifies how option works when specified multiple times:
- single: the last provided value replaces the earlier ones
- append: it supports being provided multiple times
- boolean: on/off values
- mutex: flag-like option that disable anoter flag
The 'gen.pl' script then outputs the proper and unified language for
each option's multi-use behavior in the generated man page.
The multi: header is requires in each .d file and will cause build error
if missing or set to an unknown value.
Closes#9759
If a transfer returns an error, using this option makes curl remove the
leftover downloded (partial) local file before exiting.
Added test 376 to verify
Closes#8503
