Got the OSX autobuilder back running, and finally got a OSX build up for
the 4.20130417 release. Also fixed the OSX app build machinery to handle
rpath.

Made the assistant (and `git annex sync`) sync with git remotes that have
`annex-ignore` set. So, `annex-ignore` is only used to prevent using
the annex of a remote, not syncing with it. The benefit of this change
is that it'll make the assistant sync the local git repository with
a git remote that is on a server that does not have git-annex installed.
It can even sync to github.

Worked around more breakage on misconfigured systems that don't have GECOS
information.

... And other bug fixes and bug triage.
