Don't display invalid shipping choices when there is a USPS quote error
* capture error from XML
* save error for next time checkout page is rendered
* output error (using existing action hooks ) into checkout page
* clear saved errors prior to shipping being recalculated

**Note that this is a quick (but reasonable) fix and needs to be expanded on going forward.**
updated since in phpDoc
changed function name
maybe?????
updated phpDoc
removed unnecessary assignment
Merge pull request #1286 from JeffPyeBrook/pr-1259-invalid-zip-codes-usps

Don't display invalid shipping choices when there is a USPS quote error