Add unit test for default resolver
Add failing test for setting client's resolver to None.
Allow the client to return default_resolver when the resolver attribute is set to None.
Set return_body to True by default for datatype updates.

This addresses #344, and also resolves a bug where the HTTP interface
uses 'returnbody' and not 'return_body'.
Update documentation for multiget to address #313.
Merge pull request #285 from basho/bugfix/sdc/gh285-default-resolver

Setting resolver to None should be like setting it to default

Reviewed-by: javajolt
Merge pull request #344 from basho/bugfix/344-context-handling

Consider managing context more aggressively

Reviewed-by: javajolt
Merge pull request #313 from basho/bugfix/gh313-multiget-docs

multiget does not always return RiakObjects, as stated in documentation

Reviewed-by: javajolt
Remove stray print statement.
Merge pull request #355 from basho/bugfix/stray-print-statement

Remove stray print statement.

Reviewed-by: javajolt
Add properities to cache certificiates in `SecurityCreds`