INT-2938 Filter - Provide Option for Discard

Provide an option to determine whether or not the discard
(and exception throwing if configured) occurs within the
advice chain (default), or after it completes.

INT-2938 Filter Discard Advice Option - Schema

Schema, parser, tests for option on filter element.

INT-2938 Polishing - PR Comments + Doc

INT-2938 Add to "What's New"

INT-2938 Polishing - Javadoc Typo

while merging: simplified to use boolean var only
Merge pull request #760 from garyrussell/INT-2938

# By Gary Russell
* INT-2938:
  INT-2938 Filter - Provide Option for Discard