Can use a cache for xcal exports

ChangeLog

@@ -5,6 +5,7 @@ English Dolibarr changelog
 
 For users:
 - New: Can export commercial proposals
+- New: Can use a cache for xcal exports.
 
 For translators:
 - Update some language files.

htdocs/actioncomm.class.php

@@ -597,7 +597,12 @@ class ActionComm
 
 		if ($cachedelay)
 		{
-			// \TODO Check cache
+			$now = gmmktime();
+			if (filemtime($outputfile) > ($now - $cachedelay))
+			{
+				dol_syslog("ActionComm::build_exportfile file ".$outputfile." not older than now - cachedelay (".$now." - ".$cachedelay."). Build is canceled");
+				$buildfile = false;
+			}
 		}
 
 		if ($buildfile)