ALTER TABLE set reloptions

As part of the ALTER TABLE lock reductions we've now agreed that
reloptions should have a lock level associated with them, so we can
take appropriate lock levels.

Attached patch will be applied at start of 9.5 dev cycle, so that any
new relopt authors are aware that lock levels are needed for any new
work.

Later patch will then use this infrastructure to (attempt) to reduce
lock levels, assuming no problems.

Added to next CF for June 2014, not for commit yet.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services