Bug#661947: apt-get clean deletes /var/cache/apt/*.bin

[sergio <mailbox@sergio.spb.ru>]

apt-get clean must not remove pkgcache.bin and srcpkgcache.bin !

Everyone who says 'apt-get clean' doesn't expect, that it will remove
caches, moreover it's undocumented.

Clean is suitable to run after dist-upgrade as update before.
No one will say update after clean for create caches back.

Please, return the normal behaviour back, and doesn't touch it in the
future.

If anyone wants to repair corrupted cache, there are update.

-- 
sergio.