Assorted contrib infrastructures patch

Hello,

I'm submitting 2 contrib modules and there 3 patches to core for them
from me and Martin, but they confict each other and there are some hunks
and rejections already. Here is an assorted patch of them.
Can I ask you to review the patches in this form?

- Martin's querydesc patch
http://archives.postgresql.org/message-id/490A00A8.7050708@gmail.com
- My patch for contrib/auto_explain
http://archives.postgresql.org/message-id/20081009165157.9BE4.52131E4D@oss.ntt.co.jp
- My patch for contrib/pg_stat_statements
http://archives.postgresql.org/message-id/20081027171917.ADD6.52131E4D@oss.ntt.co.jp

This is a list of modification by the patch:

- Add sourceText field in QueryDesc.
To handle query texts of nested statements in ExecutorRun_hook.

- Add DefineCustomVariable(type, variable) function.
New API to define a custom guc variable to open
config_group and flags to developers.

- Add ExplainOnePlan(outStr, queryDesc, ...) function.
Enable access to EXPLAIN output by plugin modules.

- Add force_instrument variable.
If the value is true, executor states are always initialized
with instruments. Used by auto_explain.

- Add startup_hook.
Called on server startup by startup process
where LoadFreeSpaceMap() in 8.3 had been called.

- Add shutdown_hook.
Called on server shutdown by bgwriter
where DumpFreeSpaceMap() in 8.3 had been called.

- shared_preload_libraries are loaded by auxiliary processes.
Windows port requires it.

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center