mpbb mirror-distfiles should print progress information so that slow downloads don't time out

[ryandesign (Ryan Carsten Schmidt)]

mpbb mirror-distfiles should print progress information (as MacPorts base does) so that slow downloads don't time out (as happened here):

​https://build.macports.org/builders/jobs-mirror/builds/85349/steps/mirror/logs/stdio

--->  Cleaning knp
--->  Fetching distfiles for knp
--->  Attempting to fetch knp-4.19.tar.bz2 from https://distfiles.macports.org/knp
--->  Attempting to fetch knp-4.19.tar.bz2 from http://nlp.ist.i.kyoto-u.ac.jp/nl-resource/knp/

command timed out: 1200 seconds without output running ['./mpbb/mpbb', '--prefix', '/opt/local/var/buildmaster/build/prefix', 'mirror-distfiles', '--distfiles-dir', '/Volumes/RAID/opt/local/var/rsync/macports/distfiles', 'knp'], attempting to kill

[jmroot (Joshua Root)]

In b5fdd328a05bbb70f11aa1968d3419d2ce7b84d0/mpbb (master):

mirror-multi.tcl: enable verbose output

Fixes: #58284