#23 Patch for compatibility with changes to the Safe Base

[kjnash]

Recent improvements to the Safe Base have led to the removal of several non-exported commands from the ::safe namespace. Some of these commands were called by the policy enhancement to the Safe Base in library/utils/policy.tcl.

This patch makes the plugin compatible with the changes to the Safe Base.

Changes to library/utils/policy.tcl
(1) Remove proc PolicyName
(2) In proc policy, use namespace upvar to define variable state
(3) In proc policy, set value of pname to state(policy)
pname was formerly set to [PolicyName $slave]
(4) In proc policy, replace calls to these commands, which have been
removed from the Safe Base. The "namespace upvar" formulation
allows replacement with conventional commands.
::safe::Set -> set
::safe::Unset -> unset
::safe::Exists -> info exists

[kjnash]