v.clean: fix manual for tool=rmarea

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@62048 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.clean/v.clean.html

@@ -160,8 +160,8 @@ longest boundary with an adjacent area is removed or all boundaries if
 there is no adjacent area. Area categories are not combined when a small 
 area is merged with a larger area.
 <p>
-Threshold gives area size in map units, for latitude-longitude locations
-in square meters.
+Threshold must always be in square meters, also for latitude-longitude 
+locations or locations with units other than meters.
 
 <h3>Remove all lines or boundaries of zero length</h3>
 <em>tool=rmline</em>