update ChangeLog and prepare for tagging 2.1.0beta3

git-svn-id: http://svn.osgeo.org/postgis/branches/2.1@11566 b70326c6-7e19-0410-871a-916f4a2858ee
start rc1dev cycle and switch docs back to dev site

git-svn-id: http://svn.osgeo.org/postgis/branches/2.1@11568 b70326c6-7e19-0410-871a-916f4a2858ee