Source inclusion for targets of <Embed-Dependency>

This seems like it would be rather hideous to fix, but I didn't see it anywhere and thought I would note it.

When the <Embed-Dependency> instruction is used along with the maven-source-plugin, source artifacts that otherwise exist alongside the dependency jar artifacts are not included in the source jars of the artifact being built. It's not difficult to manually add the source jars for each embedded dependency on a remote project, but gets annoying when changes to the project cause the source jar attachments to be wiped out when the project is reloaded.

It seems like it would be difficult to fix because either maven-source-plugin needs to know about the various locations that bundle instructions can live or bundle plugin needs to add sources to existing source jars. Both of of those solutions violate containment of the other plugin's role.