sweethome3d: update to latest
make vanity script less spammy
FONTCONFIG_FILE: remove setters to /etc/fonts/fonts.conf

Any reasonably new version of fontconfig does search that path by default,
and setting this globally causes problems, as 2.10 and 2.11 need
incompatible configs.

Tested: slim+xfce desktop, chrootenv-ed steam.
I have no idea why we were setting the global variable;
e.g., neither Fedora nor Ubuntu does that.
kde-workspace: Use automatic version (close #4383)

See https://github.com/NixOS/nixpkgs/pull/4265#discussion_r18430068

This should work but I didn't test it :grin:
rustcMaster: Update to more recent commit and remove patch

The patch to the tests is now included upstream. Also in this version,
an issue was fixed upstream where LTO would fail with permission denied
in NixOS.
XFCE battery plugin: new package

Closes #4386