pgsql-server: Rename XLOG_BTREE_NEWPAGE xlog record type into

Log Message:
-----------
Rename XLOG_BTREE_NEWPAGE xlog record type into XLOG_HEAP_NEWPAGE, and
shift support code into heapam.c accordingly. This is in service of
soon-to-be-committed ALTER TABLE SET TABLESPACE code that will want to
use this same record type for both heaps and indexes.

Theoretically I should have forced initdb for this, but in practice there
is no change in xlog contents because CVS tip will never really emit this
record type anyhow...

Modified Files:
--------------
pgsql-server/src/backend/access/heap:
heapam.c (r1.169 -> r1.170)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/access/heap/heapam.c.diff?r1=1.169&r2=1.170)
pgsql-server/src/backend/access/nbtree:
nbtsort.c (r1.82 -> r1.83)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/access/nbtree/nbtsort.c.diff?r1=1.82&r2=1.83)
nbtxlog.c (r1.14 -> r1.15)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/access/nbtree/nbtxlog.c.diff?r1=1.14&r2=1.15)
pgsql-server/src/include/access:
htup.h (r1.66 -> r1.67)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/access/htup.h.diff?r1=1.66&r2=1.67)
nbtree.h (r1.78 -> r1.79)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/include/access/nbtree.h.diff?r1=1.78&r2=1.79)