pgraph: Remove use of Flags struct in favour of Value API

One small step to completely cleaning up the pgraph package so that we
can eventually fix the code that would otherwise create a cycle!

util/interfaces.go

@@ -0,0 +1,27 @@
+// Mgmt
+// Copyright (C) 2013-2017+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package util
+
+// Bool returns the interface value if it is a bool, and otherwise it panics.
+func Bool(x interface{}) bool {
+	b, ok := x.(bool)
+	if !ok {
+		panic("not a bool")
+	}
+	return b
+}