[pacman-dev] Changes to v3 of makepkg error codes patch

[ivy.foster at gmail.com]

This attempt fixes the error, pointed out by brainpower, in which I
accidentally dropped in an assignment when I was trying to use one of
the error variables.

This time, this patch depends on the trivial wording patch sent
earlier today, rather than the other way around.

It also incorporates Dave's suggestions:
- The manpage no longer names the errors.
- E_PRETTY_BAD_PRIVACY is correctly documented (its scope could
  probably stand to be expanded to include actual GPG errors, but
  that's another patch).
- E_BUILD_FAILED has been renamed E_USER_FUNCTION_FAILED, though I
  kept E_PACKAGE_FAILED because as implemented, it's being used for
  exits on the packaging process as a whole, rather than for the user
  package function.
- Error code 2 is no longer skipped over, since bash doesn't actually
  *reserve* it.

Thanks to everyone for the feedback!

iff