[PATCH 0 of 3] Fixes for issue1557, issue1558

[Greg Ward]

My recent enhancement to CVS conversion (issue1558) introduced two
regressions (ooops):

  - issue1577: Failed test-convert-cvs-synthetic: output changed

  - issue1578: CVS conversion: dropping synthetic revisions can break
    merge detection

This series of patches fixes both bugs.  Note that patch 2 knowingly
breaks the tests in order to reproduce issue1578, and patch 3 fixes
the break.  If that's a no-no, just let me know and I'll fold patch 2
and 3 together.

       Greg