MAINT-7081: Make packages-formatter.py handle multi-line copyrights.

The nghttp2 autobuild package has copyright information that embeds a newline.
autobuild install --copyrights correctly produces that information onto two
lines. But that means packages-formatter.py must process any lines that do not
match its expected 'packagename: copyright' pattern as the continuation of the
preceding package's copyright information.

Since the processing for autobuild install --versions is so very similar, fold
both into the same outer loop.

Also report all duplicates for any package, instead of stopping at the first.