'sync' doesn't actually 'sync'

I did some reorganization of my PC-side music archive and expected positron to
"figure it out" during a sync.  It didn't - and it forced me to rebuild the
database (which in and of itself isn't bad, but takes a while).

Specifically, I had ripped two albums by the same artist which had different
attributions in the CDDB and therefor ended up in two different directories on
the PC:

tom petty/full moon fever
tom petty & the heartbreakers/greatest hits

Once I noticed this, I moved "full moon fever" to live under "tom petty & the
heartbreakers", updated the tags on the ogg files, and did a % positron sync

I ended up with the tracks duplicated on disk as well as in the database.  I
tried doing a positron del of the ones I didn't want as:  # positron del "tom
petty" and ran (again) into bug 385.

So it seems that sync should check for files that have been removed on the PC
side and remove them (and their database entries) from the neuros *before*
adding the database entries for newly copied files.  Further, it makes sense to
remove such files before copying new files to increase the chances that there's
enough space on the device during copy.