Move SizeOfHeapNewCid next to xl_heap_new_cid struct.

They belong together, but the xl_heap_rewrite_mapping struct was wedged
in between.
Fix bug in the new B-tree incomplete-split code.

Inserting a downlink to an internal page clears the incomplete-split flag
of the child's left sibling, so the left sibling's LSN also needs to be
updated.
Remove dead check for backup block, replace with Assert.

We don't use backup blocks with GIN vacuum records anymore, the page is
always recreated from scratch.
Doc: improve discussion of reverse+forward host name lookup in pg_hba.conf.

Fix some grammatical issues and make it a bit more readable.
Fix bug in the new GIN incomplete-split code.

Inserting a downlink to an internal page clears the incomplete-split flag
of the child's left sibling, so the left sibling's LSN also needs to be
updated and it needs to be marked dirty. The codepath for an insertion got
this right, but the case where the internal node is split because of
inserting the new downlink missed that.
Fix bugs in manipulation of PgBackendStatus.st_clienthostname.

Initialization of this field was not being done according to the
st_changecount protocol (it has to be done within the changecount increment
range, not outside).  And the test to see if the value should be reported
as null was wrong.  Noted while perusing uses of Port.remote_hostname.

This was wrong from the introduction of this code (commit 4a25bc145),
so back-patch to 9.1.
Active Directory subtree search work-around