@ --    pfnid = Parent File Name ID.
@ --    isaux = pmid IS AUXiliary parent, not primary parent
@ --
@ -- pid==0 if the file is added by check-in mid.
@ -- fid==0 if the file is removed by check-in mid.
@ --
@ CREATE TABLE mlink(
@   mid INTEGER REFERENCES plink(cid),  -- Check-in that contains fid
@   fid INTEGER REFERENCES blob,        -- New file content. 0 if deleted
@   pmid INTEGER REFERENCES plink(cid), -- Check-in that contains pid
@   pid INTEGER REFERENCES blob,        -- Prev file content. 0 if new
@   fnid INTEGER REFERENCES filename,   -- Name of the file
@   pfnid INTEGER REFERENCES filename,  -- Previous name. 0 if unchanged
@   mperm INTEGER,                      -- File permissions.  1==exec
@   isaux BOOLEAN DEFAULT 0             -- TRUE if pmid is the primary
@ );
@ CREATE INDEX mlink_i1 ON mlink(mid);