testlargetuples, based on test1, checks that large tuples are replicated
properly.
  
It creates three simple tables as one replication set, and replicates
them from one database to another.
  
Data is replicated in table1; there is a mixture of large and small tuples.

The function logswitch_start() is called shortly after replication
begins to request a log switch to test that tuples are passed properly
in both sl_log_1 and sl_log_2.

The origin node's slon is configured via slon.conf file, to verify that
this functionality works for the origin (because the logic for handling
this for the origin is separate from that for other nodes, in the test
harness).