Speed up COPY into tables with DEFAULT nextval()

Previously the presence of a nextval() prevented the
use of batch-mode COPY.  This patch introduces a
special case just for nextval() functions. In future
we will introduce a general case solution for
labelling volatile functions as safe for use.
Fix typo in comment.

Sawada Masahiko
Fix to_timestamp/to_date's handling of consecutive spaces in format string.

When there are consecutive spaces (or other non-format-code characters) in
the format, we should advance over exactly that many characters of input.
The previous coding mistakenly did a "skip whitespace" action between such
characters, possibly allowing more input to be skipped than the user
intended.  We only need to skip whitespace just before an actual field.

This is really a bug fix, but given the minimal number of field complaints
and the risk of breaking applications coded to expect the old behavior,
let's not back-patch it.

Jeevan Chalke
Remove pg_stat_statements--1.1.sql.

Commit 91484409bdd17f330d10671d388b72d4ef1451d7 should have removed this
file, not just reduced it to zero size.
Expose a routine to print triggers during EXPLAIN ANALYZE

This is so that auto_explain can use it.

Kyotaro HORIGUCHI