bapbuild doesn't work when the target is not in the same folder

[ivg]

Actually even worse it builds the plugin that is not usable and then fails with the missing dependency error (which is also quite an unclear message, e.g., which dependency).

It would be nice if we can improve the UX of bapbuild and add checks that will ensure that

1. bapbuild is called in the same folder as the target
2. there are no other plugins that are built in the same folder

and issue a nice diagnostic message.

Thanks to @bbenne10 for noticing this.