tests/test-extra-filelog-entry.out

convert: refactor sink initialisation, to remove hardcoding of hg

We also introduce options to explicitly set the source and destination
repository types.

Improve testing of corner cases a little.

adding b
   rev    offset  length   base linkrev nodeid       p1           p2
     0         0       3      0       0 1e88685f5dde 000000000000 000000000000