charmloader: log fails to file

Log all charms and bundles that failed the ingestion process. With err descriptions if possible.
Its there by default thanks to loggo. e.g. output:
2014-09-16 16:44:15 ERROR charmload_v4.loadfails main.go:111 cannot publish branch lp:~jrwren/charms/precise/sugarcrm/trunk to charm store: open /var/folders/4d/nl84n63j1fx3b4g530phf7rh0000gn/T/publish-branch-895723981/branch/metadata.yaml: no such file or directory