Typoes fixed in comments

Patches by Jochen Topf:
 https://github.com/libgeos/libgeos/pull/34
 https://github.com/libgeos/libgeos/pull/35

git-svn-id: http://svn.osgeo.org/geos/trunk@3990 5242fede-7e19-0410-aef8-94bd7d2200fb