pgsql: Show more processes in pg_stat_activity.

Show more processes in pg_stat_activity.

Previously, auxiliary processes and background workers not connected
to a database (such as the logical replication launcher) weren't
shown. Include them, so that we can see the associated wait state
information. Add a new column to identify the processes type, so that
people can filter them out easily using SQL if they wish.

Before this patch was written, there was discussion about whether we
should expose this information in a separate view, so as to avoid
contaminating pg_stat_activity with things people might not want to
see. But putting everything in pg_stat_activity was a more popular
choice, so that's what the patch does.

Kuntal Ghosh, reviewed by Amit Langote and Michael Paquier. Some
revisions and bug fixes by me.

Discussion: http://postgr.es/m/CA+TgmoYES5nhkEGw9nZXU8_FhA8XEm8NTm3-SO+3ML1B81Hkww@mail.gmail.com

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/fc70a4b0df38bda6a13941f1581f25fbb643c7f3

Modified Files
--------------
doc/src/sgml/monitoring.sgml | 15 ++-
src/backend/bootstrap/bootstrap.c | 4 +
src/backend/catalog/system_views.sql | 3 +-
src/backend/postmaster/pgstat.c | 194 ++++++++++++++++++++++++++++++-----
src/backend/postmaster/startup.c | 1 +
src/backend/replication/walsender.c | 4 +-
src/backend/storage/lmgr/proc.c | 27 +++++
src/backend/utils/adt/pgstatfuncs.c | 60 ++++++++---
src/backend/utils/init/postinit.c | 8 ++
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.h | 2 +-
src/include/pgstat.h | 26 +++++
src/include/storage/proc.h | 3 +-
src/test/regress/expected/rules.out | 9 +-
14 files changed, 305 insertions(+), 53 deletions(-)