Send reply in event of a premature exit (via throw) from fold.
Fix handling of bucket+type with MR keyfilters

Roach found this while writing tests for the Java client. If using the
JS syntax for using bucket types and keyfilters together through the PB
interface, this was broken. In the http case without security, the path
is not touched so it didn't show before.
Fix parsing of MR type/bucket + keyfilters inputs
Merge pull request #869 from basho/bugfix/handoff-fold-abort-early-2.0

Send reply in event of a premature exit (via throw) from fold.

Reviewed-by: reiddraper
Merge pull request #888 from basho/bugfix/bucket-types-and-mr-key-filter

Fix handling of bucket+type with MR keyfilters

Reviewed-by: kellymclaughlin