Merge build.cabal-new.sh into build.cabal.sh

Authored by hvr on Jun 3 2016, 3:19 PM.

Description

Merge build.cabal-new.sh into build.cabal.sh

The script now detect the cabal version and uses either the robust and
fast 'new-build'-logic (for version 1.24 or later), or falls back to the
fragile sandbox-based legacy logic.