A new release of the Windows client installer is available on the download page. It can safely be installed over your old version, so no problems there.
There are only two changes from 202 to 203 and they're technical only but mean that the two are incompatible.
A short while after this post I will release a new map maker and upgrade the dev server. You must use this 203 client to connect to these servers.
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 index.php_action=gallery;.png "Flame Hammer"){kind=small}
Oh OK. I think what happened was that at the time commit emails were being delayed and coming in random order, so that that email arrived well after the new client package was built. Two and two makes five, I guess :)
If the client was built from trunk HEAD (which at the time and for a few days before was r5076) then no. If it was built from an earlier revision, then yes, but the whole point was to build a new client from r5076, so hopefully this was done.
Isn't the protocol change r5075 going to invalidate this client as soon as the Dev server gets rebuilt on restart?