[tlbuild] new build of bibtex/bibtex8: failure when aux file is not in cwd

[François Charette]

On January 12 I retrieved the TL sources via rsync and built the 
binaries for a new version of the Arch Linux package "texlive-bin", 
which I maintain. Some users have since noticed that between the 
previous version, which was built using sources retrieved on September 
30 and the latest one, there is a regression in the behaviour of bibtex 
(and bibtex8). If the argument (the aux file) is not in the current 
directory, bibtex fails with this message:
bibtex: Not writing to /some/dir/basename.blg (openout_any = p).
I couldn't open file name `/some/dir/basename.blg'

This occurs notably with the build script of lilypond and the latex 
plugin of gedit.
See http://bugs.archlinux.org/task/17978 for details.

I checked the svn history for a possible change that might have affected 
this, but I am still clueless.
Any idea?

Thanks,
François