boolean hints don't support boolean arguments

[Charles Kerr]

hints such as "x-canonical-non-shaped-icon" and "x-canonical-private-affirmative-tint" are boolean hints, but only support string arguments.

For example see these two dbus-monitor logs: (1) http://paste.ubuntu.com/8365999/ and (2) http://paste.ubuntu.com/8366421/ . The former has a border around the icon; the latter does not.

The difference in invocation:

      dict entry(
         string "x-canonical-non-shaped-icon"
         variant boolean true
      )

vs:

      dict entry(
         string "x-canonical-non-shaped-icon"
         variant string "true"
      )