ghc-pkg/Cabal list syntax

The syntax of different tools is a bit inconsistent: In the BLAH.buildinfo files, the
values of e.g. ld-options are space-separated (but not most other list-valued entries
in BLAH.cabal). "ghc-pkg describe" lists these as exta-ld-opts (why a different name
here?), and these are *comma*-separated. I think this should be cleaned up a little
bit.

And while we are at syntax: Regardless of the list separator, we should be able to
include it into the values of the list elements, e.g. via "" or '' like shells.
The "space" behaviour ;-) of the Cabal syntax is a bit unclear to me in general
and seems to be rather ad-hoc...

Cheers,
    S.