Use double-quotes in link url attribute

Single quote was confusing po2xml

git-svn-id: http://svn.osgeo.org/postgis/trunk@13065 b70326c6-7e19-0410-871a-916f4a2858ee
files from transifex largely already translated

git-svn-id: http://svn.osgeo.org/postgis/trunk@13066 b70326c6-7e19-0410-871a-916f4a2858ee