brackup-restore config file access

[Gavin Carr]

brackup-restore is supposed to not require a brackup config file,
and ignores it even if it's available (see doc/design-decisions.txt).

I've just committed a patch to allow brackup-restore targets to 
access their section of the config file (if it's available), which
allows you to do restores without having to enter passwords (if the
original config file is available).
 
Only the ftp target has been updated so far, but that seems to work 
nicely. I'll update the others tomorrow.

A minor change required to support that was including the target 
name in the brackup metafile metadata ('TargetName'), so that we 
know which section of the config file to load for restores.

Cheers,
Gavin