When reporting whether a boolean flag was seen report the actual flags
rather than a summary count. For example, if you have option spec `h/help`
and we parse `-h --help -h` don't do the equivalent of `set _flag_h 3`
do `set _flag_h -h --help -h`.
Partial fix for #4226
While updating the `history` function to use `argparse` I realized it is
useful to define an option that can be used in three ways. First by
using the short flag; e.g., `-n NNN`. Second by using the long flag;
e.g., `--max NNN`. Third, as an implicit int flag; e.g., `-NNN`. This
use case is now supported by a spec of the form `n#max`.
This implements support for numeric flags without an associated short or
long flag name. This pattern is used by many commands. For example `head
-3 /a/file` to emit the first three lines of the file.
Fixes#4214
