Improve key representation for GIN jsonb_ops, and fix existence-search bug.

Change the key representation so that values that would exceed 127 bytes
are hashed into short strings, and so that the original JSON datatype of
each value is recorded in the index.  The hashing rule eliminates the major
objection to having this opclass be the default for jsonb, namely that it
could fail for plausible input data (due to GIN's restrictions on maximum
key length).  Preserving datatype information doesn't really buy us much
right now, but it requires no extra space compared to the previous way,
and it might be useful later.

Also, change the consistency-checking functions to request recheck for
exists (jsonb ? text) and related operators.  The original analysis that
this is an exactly checkable query was incorrect, since the index does
not preserve information about whether a key appears at top level in
the indexed JSON object.  Add a test case demonstrating the problem.

Make some other, mostly cosmetic improvements to the code in jsonb_gin.c
as well.

catversion bump due to on-disk data format change in jsonb_ops indexes.
More jsonb cleanup.

Fix JSONB_MAX_ELEMS and JSONB_MAX_PAIRS macros to use CB_MASK in the
calculation. JENTRY_POSMASK happens to have the same value at the moment,
but that's just coincidental.

Refactor jsonb iterator functions, for readability.

Get rid of the JENTRY_ISFIRST flag. Whenever we handle JEntrys, we have
access to the whole array and have enough context information to know
which entry is the first. This frees up one bit in the JEntry header for
future use. While we're at it, shuffle the JEntry bits so that boolean
true and false go together, for aesthetic reasons.

Bump catalog version as this changes the on-disk format slightly.
Fix typcategory labeling of jsonb.

Dunno who had the cute idea of labeling jsonb as typcategory 'C',
but it is not a composite type.  Label it 'U', since that's what
json is using.
Teach add_json() that jsonb is of TYPCATEGORY_JSON.

This code really needs to be refactored so that there aren't so many copies
that can diverge.  Not to mention that this whole approach is probably
wrong.  But for the moment I'll just stick my finger in the dike.
Per report from Michael Paquier.
Remove overeager assertion in logical_heap_begin_rewrite.

It's legal to configure wal_level=logical and max_replication_slots=0
simultaneously.

Andres Freund
Code review for logical decoding patch.

Post-commit review identified a number of places where addition was
used instead of multiplication or memory wasn't zeroed where it should
have been.  This commit also fixes one case where a structure member
was mis-initialized, and moves another memory allocation closer to
the place where the allocated storage is used for clarity.

Andres Freund
Get rid of bogus dependency on typcategory in to_json() and friends.

These functions were relying on typcategory to identify arrays and
composites, which is not reliable and not the normal way to do it.
Using typcategory to identify boolean, numeric types, and json itself is
also pretty questionable, though the code in those cases didn't seem to be
at risk of anything worse than wrong output.  Instead, use the standard
lsyscache functions to identify arrays and composites, and rely on a direct
check of the type OID for the other cases.

In HEAD, also be sure to look through domains so that a domain is treated
the same as its base type for conversions to JSON.  However, this is a
small behavioral change; given the lack of field complaints, we won't
back-patch it.

In passing, refactor so that there's only one copy of the code that decides
which conversion strategy to apply, not multiple copies that could (and
have) gotten out of sync.
Improve user-facing JSON documentation.

I started out with the intention of just fixing the info about the jsonb
operator classes, but soon found myself copy-editing most of the JSON
material.  Hopefully it's more readable now.
Fix broken allocation logic in recently-rewritten jsonb_util.c.

reserveFromBuffer() failed to consider the possibility that it needs to
more-than-double the current buffer size.  Beyond that, it seems likely
that we'd someday need to worry about integer overflow of the buffer
length variable.  Rather than reinvent the logic that's already been
debugged in stringinfo.c, let's go back to using that logic.  We can
still have the same targeted API, but we'll rely on stringinfo.c to
manage reallocation.

Per report from Alexander Korotkov.
Fix bogus documentation of json_object_agg().

It takes two arguments, not one.
Update config.guess and config.sub
Accept tcl 8.6 in configure's probe for tclsh.

Usually the search would find plain "tclsh" without any trouble,
but some installations might only have the version-numbered flavor
of that program.

No compatibility problems have been reported with 8.6, so we might
as well back-patch this to all active branches.

Christoph Berg
Fix bug in lossy-page handling in GIN

When returning rows from a bitmap, as done with partial match queries, we
would get stuck in an infinite loop if the bitmap contained a lossy page
reference.

This bug is new in master, it was introduced by the patch to allow skipping
items refuted by other entries in GIN scans.

Report and fix by Alexander Korotkov
More work on the JSON/JSONB user documentation.

Document existence operator adequately; fix obsolete claim that no
Unicode-escape semantic checks happen on input (it's still true for
json, but not for jsonb); improve examples; assorted wordsmithing.
Rename min_recovery_apply_delay to recovery_min_apply_delay.

Per discussion, this seems like a more consistent choice of name.

Fabrízio de Royes Mello, after a suggestion by Peter Eisentraut;
some additional documentation wordsmithing by me
docs:  Mark 9.4 release notes as current as of today
Translation updates
Rename jsonb_hash_ops to jsonb_path_ops.

There's no longer much pressure to switch the default GIN opclass for
jsonb, but there was still some unhappiness with the name "jsonb_hash_ops",
since hashing is no longer a distinguishing property of that opclass,
and anyway it seems like a relatively minor detail.  At the suggestion of
Heikki Linnakangas, we'll use "jsonb_path_ops" instead; that captures the
important characteristic that each index entry depends on the entire path
from the document root to the indexed value.

Also add a user-facing explanation of the implementation properties of
these two opclasses.
Find postgresql.auto.conf in PGDATA even when postgresql.conf is elsewhere.

The original coding for ALTER SYSTEM made a fundamentally bogus assumption
that postgresql.auto.conf could be sought relative to the main config file
if we hadn't yet determined the value of data_directory.  This fails for
common arrangements with the config file elsewhere, as reported by
Christoph Berg.

The simplest fix is to not try to read postgresql.auto.conf until after
SelectConfigFiles has chosen (and locked down) the data_directory setting.

Because of the logic in ProcessConfigFile for handling resetting of GUCs
that've been removed from the config file, we cannot easily read the main
and auto config files separately; so this patch adopts a brute force
approach of reading the main config file twice during postmaster startup.
That's a tad ugly, but the actual time cost is likely to be negligible,
and there's no time for a more invasive redesign before beta.

With this patch, any attempt to set data_directory via ALTER SYSTEM
will be silently ignored.  It would probably be better to throw an
error, but that can be dealt with later.  This bug, however, would
prevent any testing of ALTER SYSTEM by a significant fraction of the
userbase, so it seems important to get it fixed before beta.
Stamp 9.4beta1.