Wikimedia Bugzilla is closed!

Original bug title:
DjVu test spams standard output

How to reproduce:
Upload a patch set to core or run the unit tests locally.

Evidence:
https://integration.wikimedia.org/ci/job/mediawiki-core-regression-master/6741/console
16:18:32 ..........*** [1-11711] Failed to open 'some-nonexistent-file': No such file or directory.
16:18:32 *** (ByteStream.cpp:693)
16:18:32 *** 'DJVU::GUTF8String DJVU::ByteStream::Stdio::init(const DJVU::GURL&, const char*)'
16:18:32 
16:18:32 djvutxt: [1-11711] Failed to open 'some-nonexistent-file': No such file or directory.
16:18:32 djvutxt: 'ByteStream.cpp:693'

Expected:
No console spam.

Considerations so far:
ori: tim suggested that we add a 'discardStderr' option to wfShellExec()
ori: there is no command-line option to djvutxt that would make it not spam; I checked
ori: discardStderr would 2>/dev/null obviously