CSV import: "Ignore this field" can be used more than one time in the mapping.

git-svn-id: http://svn.code.sf.net/p/itop/code/trunk@3259 a333f486-631f-4898-b8df-5754b55c2be0

pages/csvimport.php

@@ -993,7 +993,7 @@ EOF
 						iOccurences++;
 					}
 				});
-				if (iOccurences > 1)
+				if ((iOccurences > 1) && (sRefValue != ':none:'))
 				{
 					$(this).parent().css({'border': '2px #D81515 solid'});
 					bResult = false;