Index: t3lib/class.t3lib_extmgm.php
===================================================================
--- t3lib/class.t3lib_extmgm.php	(revision 7724)
+++ t3lib/class.t3lib_extmgm.php	(working copy)
@@ -122,6 +122,30 @@
 	 ***************************************/
 
 	/**
+	 * Checks whether the extension with extension key $key is installed.
+	 *
+	 * @param string $key key of the extension to test, must not be empty
+	 * @param boolean $exceptionIfNotLoaded
+	 *        whether an exception should be thrown if the extension is not
+	 *        loaded
+	 *
+	 * @return boolean TRUE if the extension is loaded, FALSE otherwise
+	 */
+	public static function isInstalled($key, $exceptionIfNotLoaded = FALSE) {
+		$isInstalled = t3lib_div::inList(
+			$GLOBALS['TYPO3_CONF_VARS']['EXT']['extList'], $key
+		);
+		if (!$isInstalled && $exceptionIfNotLoaded) {
+			throw new BadFunctionCallException(
+				'TYPO3 Fatal Error: Extension "' . $key . '" was not installed!',
+				1272625953
+			);
+		}
+
+		return $isInstalled;
+	}
+
+	/**
 	 * Returns true if the extension with extension key $key is loaded.
 	 * Usage: 109
 	 *