PATCH: default_index_tablespace

Hi,

This small patch implements a new GUC (default_index_tablespace) plus
supporting code.
Originated from a customer request, the feature intends to make
creation of indexes on SSD-backed tablespaces easy and convenient
(almost transparent) for users: the DBA can just set it and indexes will
be placed in the specified tablespace --as opposed to the same
tablespace where the referenced table is-- without having to specify it
every time.

Feedback appreciated.



Thanks,

   / J.L.