fix #526: Better check for existing Doap maintainers
The current maintainers are hashed by either their email, or if that is missing, their D-L account name. However, the "identifier" of a DOAP maintainer is either their full name, or else their account name, or last their email (in that order). That means checking for that "identifier" in the current maintainers dictionary almost always fails. Since the maintainers to be removed get removed after new maintainers are added, that means maintainers get added and then removed on one run, and the next run they get added again. This flipping back and forth is not intended.
Fix this by not checking for the single "identifier", but by explicitly checking first the DOAP maintainer's email, and then otherwise their account name, in that exact order.
First commit
First commit is just because I was having a hard time formatting my (arguably quite big) commit message. I can drop it if unwanted.