Don't generate existing R

[william-ferguson-au]

Don't generate R.java if one has already been generated for that package in the compile classpath.
This stops extra R javas being generated for a test-apk that will mirror those from the target APK.

[william-ferguson-au]

@mosabua could you check over and merge this please.

[mosabua]

lgtm - wanna add a changelog entry ? Then I can merge and if you want cut a new release

[william-ferguson-au]

Done. Ta

[mosabua]

need a release?

[william-ferguson-au]

No :-) I generally run off my own version until the AMP releases catch up with me.
Have been thinking that we need to overhaul all the Mojos and remove the unnecessary implementation inheritance. It's polluting the params for almost all the Mojos so that it's really not clear what params a Mojo actually needs or cares about.

This is especially problematic when you look at the doco in the generated goals.