In using several of the sendmail configuration
databases as for example virtusertable.db, access.db
etc. it would be nice to be able to process more than
one source file; one example is: a handwritten access
file and a spammer table obtained from some internet
source; another would be: combining an automatically
generated virtusertable with a handwritten one.
Such behaviour is consistent with the usual makemap
semantics, which uses input from stdin and thus allows
multiple input files for each db.