Extend namedserverfilter so that it is possible to use as target

• master,
• slave,
• uptodate server, and
• a specific set of servers
  in addition to the current possibility of specifying a particular server.

Also make it possible to specify several regexes and targets for a single filter.

The current behaviour of

match=some string

server=server2

should be retained but can be mutually exclusive with a new way of specifying several regexes and targets, for instance, like:

match1=some string

target1=server1

match2=some string

target2=->master

match3=some string

target3=->slave

match4=some string

target4=server1,server2,server3