Adds the "--p4-passwd" command line option to allow a user to supply the Perforce Ticket or clear-text password.  This is useful in cases where the Perforce password/ticket is not available in the environment when the command is run (such as, when this command is part of an automated script).

Tested with the Perforce ticket, and worked as expected.  Using the clear-text password should also work, but requires the user to be allowed to supply the password in that format, which isn't always the case.