Added check_plugin_version() function

ChangeLog

@@ -135,6 +135,7 @@ Version 1.5.2 - CVS
   - Added APOP, TLS and STLS support to mail_fetch plugin (#575299).
   - Added Courier IMAP OUTBOX check to configtest utility.
   - Moved login_form hook to its own table row on login page.
+  - Added check_plugin_version() function
 
 Version 1.5.1 (branched on 2006-02-12)
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