bug#19296: [PATCH] Package archives now have priorities.

[Stefan Monnier]

> The part where M-x package-install RET foo RET will install foo-1.2.3 over
> foo-20141205.315 when the latter is only available from a repository
> with a lower priority, and where "U" in the package list will not upgrade
> foo-1.2.3 to foo-20141205.315 when the latter is only available
> from a repository with a lower priority.

So there are two part above:
- decide which repository to use when M-x package-install is used.
- don't switch repository for upgrade.

I don't think we need priorities for the second part once we refrain
from automatically switching from one repository to another during
upgrade.  For the first part priorities could still be useful, indeed,
tho we should simply prompt the user for those cases where there is
a choice between several repositories.

So, overall, I'm not sure having repository priorities would be really
important, but the patch is fairly small, so I think it's OK.  BTW,
please simplify the patch by removing package-archive-default-priority
(and hard code 0 as the default priority).


        Stefan