Since the last commit will force rebuilds of all depends, take the opportunity
to clean up a few other things that would trigger rebuilds as well.
- Move source stamps to the sources dir so that SOURCES_PATH is respected for
"make download".
- Only print "fetching..." when actually downloading a file.
- Avoid using non-deterministic paths for the recipe hash (patch location).
This should ensure that all builders get the same resulting build-ids.
- Use a per-package source paths. This will allow for removing old source files
in the future.
- Use a host-agnostic path for downloads which gets cleaned up properly.
Some sources are renamed after download, since the filenames don't play nice
with (for example) gitian. This fixes the rename.
Needed for OSX build as it renames a file.
