xcpdb: new tool which wraps Xapian's copydatabase(1)
copydatabase(1) is an existing Xapian tool which is the
recommended way to upgrade existing DBs to the latest Xapian
database format (currently "glass" for stable/released
versions). Our use of Xapian relies on preserving document IDs,
so we'll wrap it like we do xapian-compact(1) and use the
"--no-renumber" switch.
I could not name the tool "public-inbox-copydatabase" since it
would be ambiguous as to which DB it's actually copying. So, I
abbreviated the suffix to "xcpdb" (Xapian CoPy DataBase), which
I hope is acceptable and unambiguous.