In which cases is a descmsg needed?
When extension name and description message key differ: In this case they are equal after some normalization by the Translate extension: Stripping spaces and lowercasing all: "Fundraiser Landing Page" -> "fundraiserlandingpage" .... wait...
Now I see why you ask: You named the message key: 'fundraisinglandingpage-desc'. That fails. Either rename the message key to 'fundraiserlandingpage-desc' or add a line with descmsg to mediawiki-defines.txt. For consistecy I prefer the first solution.
I was really askign because this knowledge doesn't seem documented anywhere (eg. at /trunk/translatewiki/README). Only a few ones really know how to completely add a extension/message. (FIXED)