cabal sdist trouble with GHC from head

[Sven Panne]

2014-10-23 15:01 GMT+02:00 Alan & Kim Zimmerman <alan.zimm at gmail.com>:
> cabal has changed for HEAD, you need to install 1.21.1.0

Hmmm, so we *force* people to update? o_O Perhaps I've missed an
announcement, and I really have a hard time deducing this from the
output on Travis CI. Is 1.21.1.0 backwards-compatible to previous
GHCs? Or do I have to set up something more or less complicated
depending on the GHC version (which would be unfortunate)?