Fixing small errors in USPS settings page
The label on the USPS shipping options didn't match the input id
because of what seems like a typo. That's fixed. I also fixed the
shipping options not reflecting in the form properly, by casting the
returned value of array_search (the index it was found at) to a bool
to make it comparable internally in the checked() function
Merge pull request #609 from zirwin/master

Fixing small errors in USPS settings page