[aur-dev] URL redirect should be set to the merged package

[郑文辉(Techlive Zheng)]

Currently, if a package gets merged into another package, the URL link
to the merged package will say 404, this should not happen, instead, a
redirection should be made to the package that was merged into.

If a new package with the same name as the merged package is uploaded
again, then, the redirection will be removed.

Which means, there should be a record of the merging activities. When
a package is being queried, if the package exists then just return it,
if not, check the merging records for the latest merging record, and
redirect the page to the new package.