[TYPO3-english] Accessing extension constant from php script

[Jackie Stallard]

I've created an extension constant in ext_conf_template.txt and I can 
see it from the extension manager.

According to the documentation I should be able to access the constant 
in my PHP script as follows:
$GLOBALS['TYPO3_CONF_VARS']['EXT']['extConf']['austcom_merge']['austcom_mergeDb']
(where austcom_merge is the name of my extension and austcom_mergeDb is 
my constant.)

But there is no 'austcom_merge' tree in 
$GLOBALS['TYPO3_CONF_VARS']['EXT']['extConf']. Other extensions are 
listed - but not austcom_merge.

Have I missed a step?

I've also tried placing the constant in ext_localconf.php as follows:
$TYPO3_CONF_VARS['EXTCONF'][$_EXTKEY]['austcom_mergeDb'] = 'newprojman';
Again, there is no 'austcom_merge' tree under $TYPO3_CONF_VARS['EXTCONF']

Can anyone help?
Thanks

Jackie