Clarify column iterator usage

getColumnIterator expects position in sequence coordinates (genome coordinates if the sequence is a genome), but ColumnIterator->toSite expects the position exclusively in genome coordinates.

api/inc/halSegmentedSequence.h

@@ -82,7 +82,7 @@ class SegmentedSequence
     * * (note that other genomes in their spanning tree will be
     * * traversed as necessary but not reported)
     * @param maxInsertLength maximum insertion to be traversed
-    * @param position Index in genome of returned iterator 
+    * @param position Index in sequence of returned iterator 
     * @param noDupes Don't follow paralogy edges
     * @param noAncestors Don't report any non-leaf nodes in output
     * @param reverseStrand Map from reverse strand of this sequence