Fix a few things in makeahpkg.

1. The commenting-out of repos is a bit peculiar in that a single level of
commenting is removed when the pacman.conf is pushed into the chroot.
2. Add a trap on ERR to make errors non-silent, though they still are very
non-descriptive.
3. Do not install `haskell-haddock`, because it isn't needed and doesn't
exist.
4. Clean the build chroot after creating the root, just to make sure it
happens.

Signed-off-by: Magnus Therning <magnus@therning.org>