Alexis S. L. Carvalho <alexis@cecm.usp.br> [Sat, 01 Sep 2007 02:49:18 -0300] rev 5279
convert: clear the dirstate before a conversion, invalidate it afterwards
Clearing it before the conversion protects us from whatever data were
there (file copies in particular).
Invalidating it after the conversion avoids writing a possibly
inconsistent dirstate to disk.