Avoid importing changesets of closed Bitbucket PRs
Importing changesets for merged PRs should just do nothing, but they are occasions to fail in weird ways if there's ever a bug while importing them an forcing new changesets to topics. Not even to speak that importing thousands of changesets with an expected void result is a waste of time and resources.
Old PRs that have been declined can be really ugly, and jeopardize the whole import process. For instance PyPy has a PR that brings over 30000 changesets. According to the comments, Bitbucket didn't like it either.
This should find its way into Heptapod 0.7.x, but a first fix will be in 0.8.0. At some point, we may have a flag for people that insist on importing declined PRs but that's not urgent.