Have ALTER CONSTRAINT recurse on partitioned tables

Fix OID passed to object-alter hook during ALTER CONSTRAINT

Fix race condition between shutdown and unstarted background workers.

Rethink the "read/write parameter" mechanism in pl/pgsql.

Remove PLPGSQL_DTYPE_ARRAYELEM datum type within pl/pgsql.

Re-implement pl/pgsql's expression and assignment parsing.

Add the ability for the core grammar to have more than one parse target.

Suppress log spam from multiple reports of SIGQUIT shutdown.

Improve client error messages for immediate-stop situations.

Use setenv() in preference to putenv().