apk cache sync does not exit with error if cache media gets full

To reproduce:

create a loopbackdevice that is very small, mount it, and create the apk cache symlink to there. then run apk cache sync.

You will not get any error messages and apk exists with success.

tested with apk-tools-2.1.0

(from redmine: issue id 666, created on 2011-05-27, closed on 2011-10-21)

• Changesets:
  • Revision 9cb0ce54 by Timo Teräs on 2011-07-11T08:22:26Z:

cache: return error if cache sync or download fails

fixes #666