convert: Use clone's behaviour for the default destionation name. Adjusted the documentation for this and for the fact that the destionation is created even if a name is specified.

#!/bin/sh

hg init
echo a > a
hg ci -Am t

hg mv a b
hg ci -Am t1
hg debugrename b

hg mv b a
hg ci -Am t2
hg debugrename a

echo % test with --rev
hg debugrename --rev 1 b