lib: change RBUriRecurseFunc to take a GFileInfo

This lets callers get more information about the things being recursed
through without overcomplicating the interface.
lib: add rb_file_resolve_symlink

Like rb_uri_resolve_symlink, but taking and returning a GFile rather than
a uri string
import-job: resolve symlinks before adding to the import job

RhythmDB resolves symlinks internally, so files will appear under the
canonical location rather than what we get from the uri recurser.
If we add the non-canonical location to the import job, the job will never
finish.