[revamp] p4a silently fails if --private is not absolute

[str4d]

This one tripped me up for a while, because the documentation (both master and revamp) was not clear on where the entry point to the Python code should go. But eventually I discovered that if --private is given a relative path (on Linux), it silently fails: assets/private.mp3 is successfully built without any of the app code, resulting in an APK that installs but doesn't start.

Either --private should be extended to support relative paths, or the documentation should say they aren't supported, and p4a should fail loudly.

[inclement]

This is just a bug, relating to how p4a switches directory contexts - it holds the correct directory for relative path resolution in a variable but doesn't always correctly apply it. Thanks for reporting it.

[inclement]

(Oops, wrong issue)

[inclement]

This should be fixed by dfc8ab3