bug#17831: 24.4.50; bad default value for `Man-width'

[Stefan Monnier <monnier@iro.umontreal.ca>]

> Using the same approach like processing escape sequences in grep/compilation
> produces a nice result for M-x man: it displays the first formatted page
> immediately and continues formatting the rest of the man page in background.
> There are still small details to iron out but this is basically achieved
> with the following patch.

Looks good.

> There is one problem that I noticed on large man pages: formatting
> small chunks by process-filter is little slower than formatting the
> whole output like it currently does.

That's expected.

> Could it be possible that a slowdown is caused by `narrow-to-region'?

`narrow-to-region' is cheap.  But doing it by chunks is necessarily
slower, because there is a non-negligible overhead "per chunk".
`narrow-to-region' is part of that overhead, but there are others much
more costly, such as going through redisplay (which may even sometimes
have to update some part of the display, such as the "nn%" thingy since
that depends on the total buffer size).


        Stefan