merge pick and scan

[Philipp Takacs]

Hi

To scan selected messages currently a combination of scan and pick
is used. It would be nice to be able to write something like:

> scan -from bob

In order to do this we could add the -form/-format switches to pick and
make scan a link to pick. To avoid most breakage pick would use "%(msg)"
format by default and scan.default if called as scan. This way only some
scan aliases would break (if -form/-format is not explicitly set for them).
All other usages would still work. It would still be possible to call:

> scan `pick -from bob`

I have implemented this for mmh and could port it to nmh. What do you
think of the idea?

Philipp