Add transient plugin, which adds ~/.ikiwiki/transient as an underlay

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IkiWiki/Plugin/transient.pm

@@ -0,0 +1,33 @@
+#!/usr/bin/perl
+package IkiWiki::Plugin::transient;
+
+use warnings;
+use strict;
+use IkiWiki 3.00;
+
+sub import {
+	hook(type => "getsetup", id => "transient",  call => \&getsetup);
+	hook(type => "checkconfig", id => "transient", call => \&checkconfig);
+}
+
+sub getsetup () {
+	return
+		plugin => {
+			# this plugin is safe but only makes sense as a
+			# dependency; similarly, it needs a rebuild but
+			# only if something else does
+			safe => 0,
+			rebuild => 0,
+		},
+}
+
+our $transientdir;
+
+sub checkconfig () {
+	eval q{use Cwd 'abs_path'};
+	error($@) if $@;
+	$transientdir = abs_path($config{wikistatedir})."/transient";
+	add_underlay($transientdir);
+}
+
+1;