Relegated previous support for "p4 diff" to the bottom drawer and
use the Diff class provided in the P4 API to send the diff listings
through the OutputText() interface. This has two main advantages over
the old implementation: (a) same output as "p4 diff" as it uses the
same classes and (b) doesn't require extra perl modules.
The old implementation is still available - you just have to
call P4::Client::DoPerlDiffs() to specify your preference.