Statistics for databases, indexes and functions

[gleu]

Here are three patches for statistics on various objects:

• database: we had statistics on the Databases node but we didn't have them on each individual database node.
• indexes: we had statistics on each individual index node but we didn't have them on the Indexes node of each table.
• functions: we didn't have them at all, but it is now needed on 8.4.

I did a patch for each one because I'm not sure they will all be accepted right away. For the database one, I'm not sure that copying the DisplayStatistics?() function code is the better way to make it work. On the index one, should I also display statistics for primary key and unique constraints? it seems it would be a good idea. But it would meant that only these constraints would be displayed. CHECK constraints, for example, would be invisible. Comments?

[gleu]

r7981