flatten: Fix undefined error, because node.minifiedSource sometimes can be undefined.
Bundle flattening logging fix

This fixes a problem that was occuring when flattening bundles. We were
passing in an array of bundle string names to name.getName, where
name.getName actually expects the bundle itself.
Exclude plugins for global pluginified files

This adds an option to concatSource to allow the exclusion of plugins
from the bundle.source. This is necessary because o plugins that are not
meant to be included in the build, a `System.set` call is added which
will not work for global pluginified outputs. Fixes #42
Merge pull request #63 from matthewp/multi-build-errors

Fixes for multi build errors
Merge pull request #62 from matthewp/exclude-plugins

Exclude plugins for global pluginified files