rebase: add test to demonstrate an issue in dry-run
In dry-run mode, the case when there is nothing to rebase
is not handled correctly. Added test show that it try to
abort a rebase while there is no rebase in progress.
This will be fixed in next patch.
Differential Revision: https://phab.mercurial-scm.org/D9658
edge: ({col}, {row}) -> ({nextcol}, {nextrow}) (color {color})