Distinguish redactions from the string "REDACTED" in formatRedactedTrace

Distinguish redactions from the string "REDACTED" in formatRedactedTrace

In the output of MWExceptionHandler::formatRedactedTrace, it is not
possible to determine (without checking the configuration) whether arg 0
in "foo('REDACTED')" was redacted or was merely passed the string
"REDACTED".

This patch changes redaction to instead output "foo(REDACTED)" in the
case of redaction. This parallels the situation with arrays and objects,
where for example "foo(Array)" was passed an array while "foo('Array')"
was passed the string "Array".

Change-Id: Ia2a761687c69b630afa3ccd8668b06b28e3ecdd3