Use more descriptive message when disk is out of space

[22:55] rxu: bantu : 'ATTACH_QUOTA_REACHED' => 'Sorry, the board attachment quota has been reached.', is used for exceeding attachment quota as well as for exceeding disk space.
[22:55] rxu: for the latter one the description is unrelated and confusing actually.
[22:55] rxu: shall we fix that?
[22:55] bantu: I think it's okay.
[22:56] rxu: adjusting the quota doesn't fix the issue if out of disk space
[22:57] rxu: so user have to guess what's the cause of the thing.
[22:57] bantu: I don't think users should know that the filesystem has run out of space.
[22:58] rxu: then we should probably notify administrator about that?
[22:59] naderman: bantu: what's the harm?
[22:59] rxu: or even through a notice on ACP main
[22:59] bantu: naderman: it's embarrassing
[22:59] naderman: uh
[22:59] naderman: who cares
[22:59] naderman: if it happens, it happens
[23:01] naderman: certainly not important enough to spend much time on
[23:01] naderman: just changing the message is enough

[23:11] rxu: what about new language entry for 'not enough disk space to post attachments' thing?
[23:13] rxu: example: http://www.phpbb.com/community/viewtopic.php?f=46&t=1884485