Handle case of hudson.Extension doesn't already exist for Eclipse.

re: only catch IOException when using Eclipse filer:
- good idea. done

re: apply message to each associated item
- good idea. done

re: you didn't file a pull request
- ok. doing that now

Note, I've also purged a META-INF/services file, which I think is now obsolete? and causes a build error on eclipse ("IndexerFactory not found")