Correctly align page's images in generic wal API
Correctly align page's images in generic wal API

Page image should be MAXALIGN'ed because existing code could directly align
pointers in page instead of align offset from beginning of page.

Found during play with indexes as extenstion, Alexander Korotkov and me

xinzweb/gpdb,50wu/gpdb,adam8157/gpdb,xinzweb/gpdb,greenplum-db/gpdb,lisakowen/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,adam8157/gpdb,adam8157/gpdb,ashwinstar/gpdb,xinzweb/gpdb,xinzweb/gpdb,jmcatamney/gpdb,50wu/gpdb,ashwinstar/gpdb,50wu/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,adam8157/gpdb,adam8157/gpdb,greenplum-db/gpdb,lisakowen/gpdb,lisakowen/gpdb,xinzweb/gpdb,lisakowen/gpdb,adam8157/gpdb,jmcatamney/gpdb,50wu/gpdb,50wu/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,50wu/gpdb,jmcatamney/gpdb,50wu/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,lisakowen/gpdb,xinzweb/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,greenplum-db/gpdb