bndmanifest and java-library intermodule dependencies

In https://github.com/diffplug/durian-swt/pull/7/commits/496386ecebd023075b03a041d238af8d02a29469 I used `java-library` in a multi-module project, and I declared an `api` dependency on another module within the project. I then saw intermittent errors like [this](https://travis-ci.org/diffplug/durian-swt/builds/636211276#L237):

```
> Task :durian-swt:jar FAILED
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':durian-swt:jar'.
> A Jar can only accept a file or directory that exists: /home/travis/build/diffplug/durian-swt/durian-swt.os/build/libs/durian-swt.os-3.3.0.jar
```

The workaround is https://github.com/diffplug/durian-swt/pull/7/commits/b3df3311d6ef3d6ce22756512a7e742227091e3c

Inizia dalla build Travis fallita nell’attività :durian-swt: indicata e confronta l’errore segnalato con il commit di workaround in diffplug/durian-swt. Traccia il modo in cui la dipendenza api di java-library e bndmanifest gestiscono il JAR intermodulo, quindi verifica che l’errore dovuto all’assenza del JAR non si verifichi più in una build comparabile multi-modulo.

Scritto dal modello di indicizzazione a partire dal testo della issue.