Build function return fix

I've been building a script around `ccm` to run over a list of packages and build any that are out of date.  In the process, I've discovered that the `build()` function (or `ccm s`) has a non-zero return value whenever you build something that is not in the local (non-chrooted) pacman package cache, even if the build ran successfully.

For me, this is undesirable from a scripting perspective, and I assume that this isn't your intent.  The fix is very simple, and added in commit 4ca9b36

The only other source of error that this may miss is a problem during the `repo-add` command, which currently is not checked for.  I think I will submit a different pull request fixing that, since that is a separate issue and I'm not sure how you would like to handle that.  EDIT: I've submitted a fix for this in #8.

Let me know if you would like me to do something differently, I would be happy to modify the pull request.

Cheers.