Revert "Removed OTEnvelope::(Get|Set)AsBookendedString."

This reverts commit da6ef5bba4f5422dac4be4b24672f7bf7a8377f2.
Merge pull request #306 from benma/revert

Revert "Removed OTEnvelope::(Get|Set)AsBookendedString."
Fix some -Wshadow warnings.