RFC: Add option --quiet=LEVEL to disable output

[Jari Aalto]

To make bzr work from scripts, the current verbosiness is geares towards
interactive user. Let's say:

    1. Download tarball
    2. Unpack
    3. put it in bzr (bzr init)a
    4. Add file (bzr add)
    5. Put automatic commit message, derived form version (bzr ci)

All those operations the script can do by itself. If the commands (or
bzr itself) would have:

    --quiet

or
    --batch

that notify that there is no user to talk to, so all outputs other
than errors should not be displayed. I think this woudl be one of those
fmailiar "cvs global options" that precede the actual commands, like

    bzr <global options> <command> <command options>

    <global options> ::= --batch

Jari