Reduce SP memory usage

This contributed patch came from Jerome Brauge. Please find the patch attached.

As stored procedures seems to be very memory aggressive, I found two possible optimizations to avoid having three strings containing the stored procedure code in memory.

Probably, same optimizations may be applied to packages.
I haven’t add any tests because I think everything is covered by the existing tests.

What do you think about ?

In a second time, I think working on SP cache.

Currently it’ s a simple hash table and all the hash table is flushed as soon as the threshold (stored_program_cache) is reached.

It's not very good.

We could :

• Use a more intelligent cache (LFU ?)
• Add some performance counters

Regards.