[development] Caching, caching, caching...

[Khalid B]

Regarding pre-caching of aliases, the problem is that this
does not  scale. Up until 4.6 we read all the aliases in
one query, and the expensive part was not the SQL
query but the building  of the associative array for
sites with a large number of aliases.

If we cache a large number of aliases, I gues they
have to be serialized/unserialized, and then we will
be back to the same problem as before, that was
solved by individual queries.