Consider using a predictable path for downloads

[asgrim]

It downloads it to /tmp/pie_downloader_66599d860c5bc9.02217405/xdebug-xdebug-b8a7e3e — it would be nice that instead of the postfix b8a7e3e it used the git tag associated with that commit hash.

This is actually the path inside the zip that GitHub gives from the release, so we don't control that part. That said, we could add additional step to move it. Also, we may want to consider using a predictable path, e.g. $HOME/.pie/sources/xdebug/xdebug/3.4.0alpha1/ instead of a random path.

[derickr]

I think these should be downloaded to /tmp and not $HOME/.pie, but having a predictable path is very useful.

Especially when debugging crashes, as the path is in the symbol information that gdb outputs.

A random value is probably still worth keeping in a higher level path, to avoid race conditions if PIE gets run twice at the same time.

[asgrim]

This is going to be moved as part of #48 anyway, so will close this now.