resolve issue #1

Squashed commit of the following:

commit 66f27ab27c18f832aefdda585d3341a756eaf5a8
Author: Badi' Abdul-Wahid <abdulwahidc@gmail.com>
Date:   Sun Mar 31 23:58:15 2013 -0400

    nicer failure message

commit adf7c1e78967dc9ebd003e9c42fceef7a92cfcd6
Author: Badi' Abdul-Wahid <abdulwahidc@gmail.com>
Date:   Sun Mar 31 23:53:00 2013 -0400

    don't greedily fail when checking build depends