Replace "+" in object queries with "%2B"

This fixes issue #259 in which objects with "+" in the
object key cannot be retrieved.
Added test case for %2B-expansion of "+" in object names

It turns out that req.URL is already processed, so it would
come back as "has+plus" both with and without the fix, but req.RequestURI
is not %-expanded so works to verify this fix.
Merge pull request #260 from dkolbly/master

Replace "+" in object queries with "%2B"