Extensions, patch 22 (cleanup, review, cleanup)

Hi,

>From last round of review from Robert and Álvaro, here's the patch
version 22. Changes:

 - cleanup contrib/ and 'Adjust search_path' comments
 - remove contrib/*/uninstall* scripts
 - add some documentation to the NO USER DATA option
 - remove objects locking in the pg_extension_objects() SRF, per Robert
 - propose split patches

It so happens that git allows to prepare diffs for subdirs (or files) of
a tree, so I've been using that to separate away contrib changes from
the others.  As a result, 3 patches are attached: full, contrib only,
doc and src only.

Regards,
--
Dimitri Fontaine
http://2ndQuadrant.fr     PostgreSQL : Expertise, Formation et Support