Fix appender's extend
Cover 12428
Merge pull request #2076 from monarchdodra/appenderExtend

Fix Appender extend
Fix Issue 11308 - Don't use Voldemort types for std.process output

So that the return type of `execute` and `executeShell` are compatible.
Merge pull request #2085 from monarchdodra/processRet

Fix Issue 11308 - Don't use Voldemort types for std.process output