transcode: new package

Suite of command line utilities for transcoding video and audio codecs,
and for converting beween different container formats.

http://www.transcoding.org/
Merge pull request #3052 with some additional changes
Allow selection of named SF dirs
Adding libatomic_ops
Adding librevenge: a library for creating file importers
Adding libe-book: a library for importing reflowable e-book formats
Adding libmwaw: a library to import some old Macintosh text document formats
Adding libodfgen: a library for writing ODF
twelf: Fix the source URL
gperftools: Support Darwin
nix: propagate boehmgc
Add nix-plugins package
git-remote-add: new package added
support for nixos test names
name nixos tests, close #3078
structured-haskell-mode: 1.0.2 > 1.0.3