Recipe builds dep-wait incorrectly when build-dependencies are present but uninstallable

https://code.launchpad.net/~damien-moore/+archive/ubuntu/codeblocks-stable/+recipebuild/1126247 was set to dep-wait on libwxgtk2.8-dev. However, this is incorrect; it should have been a build failure instead. The apt output was:

The following packages have unmet dependencies:
 builddeps:codeblocks : Depends: libwxgtk2.8-dev but it is not going to be installed

This indicates that this package is present but uninstallable. As such, dep-waiting is incorrect. We should do the same thing as is done in the binarypackage manager, and probably put some of the necessary code in a common base class.