Initial import of tasks application

This initial import is a heavily modified version of the code I had
here, as Arse was modified for other purposes in the meantime and the
application no longer worked with it.

In addition:
 * I did not import the user management part yet,
 * task dependencies are supported in-base, but there is no interface
for that yet.

includes/t-items/fields.inc.php

@@ -0,0 +1,44 @@
+<?php
+
+
+class Item_LocationField
+	implements FieldValidator , FieldModifier
+{
+
+	private $okLocations;
+
+	public function __construct( $okLocations )
+	{
+		$this->okLocations = $okLocations;
+	}
+
+	public function replace( $value )
+	{
+		$exploded = explode( ':' , $value );
+		if ( count( $exploded ) != 2 ) {
+			$exploded = array( 0 , $value );
+		}
+
+		if ( $exploded[ 1 ] == '' ) {
+			$exploded[ 0 ] = 1;
+		} else {
+			$exploded[ 0 ] = ( $exploded[ 0 ] == '0' ) ? 0 : 1;
+			$exploded[ 1 ] = (int) $exploded[ 1 ];
+		}
+
+		return join( ':' , $exploded );
+	}
+
+	public function validate( $value )
+	{
+		list( $inside , $before ) = explode( ':' , $value );
+		if ( $before != '' && Loader::DAO( 'items' )->get( $before ) == null ) {
+			return array( 'This item no longer exists.' );
+		}
+		if ( ! ( empty( $this->okLocations ) || in_array( $value , $this->okLocations ) ) ) {
+			return array( 'Invalid destination' );
+		}
+		return null;
+	}
+}
+