pgsql: Move BufferGetPageSize and BufferGetPage from bufpage.h to

Log Message:
-----------
Move BufferGetPageSize and BufferGetPage from bufpage.h to bufmgr.h. It is
more logical that way, and also it reduces the amount of unnecessary includes
in bufpage.h, which is widely used.

Zdenek Kotala.

My previous patch to bufpage.h should also have credited him as author, but I
forgot (sorry about that).

Modified Files:
--------------
pgsql/src/backend/access/gin:
ginentrypage.c (r1.14 -> r1.15)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/gin/ginentrypage.c?r1=1.14&r2=1.15)
pgsql/src/backend/access/heap:
heapam.c (r1.257 -> r1.258)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/heapam.c?r1=1.257&r2=1.258)
hio.c (r1.70 -> r1.71)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/hio.c?r1=1.70&r2=1.71)
pruneheap.c (r1.12 -> r1.13)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/pruneheap.c?r1=1.12&r2=1.13)
rewriteheap.c (r1.12 -> r1.13)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/rewriteheap.c?r1=1.12&r2=1.13)
pgsql/src/backend/access/transam:
xlog.c (r1.312 -> r1.313)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xlog.c?r1=1.312&r2=1.313)
xlogutils.c (r1.53 -> r1.54)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/xlogutils.c?r1=1.53&r2=1.54)
pgsql/src/backend/commands:
analyze.c (r1.121 -> r1.122)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/analyze.c?r1=1.121&r2=1.122)
pgsql/src/backend/storage/buffer:
bufmgr.c (r1.230 -> r1.231)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/buffer/bufmgr.c?r1=1.230&r2=1.231)
pgsql/src/include/storage:
bufmgr.h (r1.111 -> r1.112)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/bufmgr.h?r1=1.111&r2=1.112)
bufpage.h (r1.80 -> r1.81)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/bufpage.h?r1=1.80&r2=1.81)