Grammar corrections from Eric Theise - https://github.com/erictheise/postgis/commit/b76aeaf6b2539345d44f3c2d60fbd84625e3467d

git-svn-id: http://svn.osgeo.org/postgis/trunk@13142 b70326c6-7e19-0410-871a-916f4a2858ee