switch from osmosis to pyosmium for updates

Pyosmium comes with convenient functions for finding the
right state and does not require external files for
rembering the state. Updates can now conveniently
set up by simply running ./utils/update.php --init-updates
and state is kept directly in the import_status table.

This change requires an update in the database schema.
Run the following to update:

ALTER TABLE import_status ADD COLUMN sequence_id integer;
ALTER TABLE import_status ADD COLUMN indexed boolean;
ALTER TABLE import_osmosis_log ADD COLUMN batchseq integer;

lib/lib.php

@@ -33,6 +33,18 @@ function getCacheMemoryMB()
     return (int)($aMatches[1]/1024);
 }
 
+function getDatabaseDate(&$oDB)
+{
+    // Find the newest node in the DB
+    $iLastOSMID = $oDB->getOne("select max(osm_id) from place where osm_type = 'N'");
+    // Lookup the timestamp that node was created
+    $sLastNodeURL = 'http://www.openstreetmap.org/api/0.6/node/'.$iLastOSMID."/1";
+    $sLastNodeXML = file_get_contents($sLastNodeURL);
+    preg_match('#timestamp="(([0-9]{4})-([0-9]{2})-([0-9]{2})T([0-9]{2}):([0-9]{2}):([0-9]{2})Z)"#', $sLastNodeXML, $aLastNodeDate);
+
+    return $aLastNodeDate[1];
+}
+
 
 function bySearchRank($a, $b)
 {