Review 28159

C. Thomas Tyler
Made former '-n' preview mode the default behavior.
Added new '-y' flag to execute a real upgrade.

Added a message in preview mode to clarify that no actual
upgrade is performed.

Removed the '-n' preview option, as preview mode is now the
default behavior.
#1: Change 28158 committed into //guest/perforce_software/sdp/dev 3 0 0
Tip: Use n and p to cycle through the changes.