absorb: make it explicit if empty changeset was created
If the config rewrite.empty-successor=skip is set, a message "became empty and was dropped" is shown if the changeset became empty. If the config rewrite.empty-successor=keep is set, absorb may create changesets even if they became empty. It’s probably a good idea to make that explicit. Therefore the message is changed to be a combination of both: "became empty and became ...". Repeating the word "became" is not very elegant. This results from the fact that "became" was and is overloaded to indicate both the change from non-empty to empty and the successor relation. In the combinated message, both meanings are used in one sentence.