Add rudimentary checking for the zip command.

(cherry picked from commit f134754c2583647bcbf0c65c31efadb469b1eca2)

htdocs/export/index.php

@@ -39,6 +39,11 @@ $exportplugins = plugins_installed('export');
 if (!$exportplugins) {
     die_info(get_string('noexportpluginsenabled', 'export'));
 }
+if (!is_executable(get_config('pathtozip'))) {
+    log_info("Either you do not have the 'zip' command installed, or the config setting 'pathtozip' is not pointing at your zip command."
+        . " Until you fix this, you will not be able to use the export system.");
+    die_info(get_string('zipnotinstalled', 'export'));
+}
 
 foreach ($exportplugins as $plugin) {
     safe_require('export', $plugin->name);

htdocs/lang/en.utf8/export.php

@@ -42,5 +42,6 @@ $string['unabletoexportportfoliousingoptions'] = 'Unable to export a portfolio u
 $string['unabletogenerateexport'] = 'Unable to generate export';
 $string['viewstoexport'] = 'Views to export';
 $string['whatdoyouwanttoexport'] = 'What do you want to export?';
+$string['zipnotinstalled'] = 'Your system does not have the zip command. Please install zip to enable this feature';
 
 ?>