Modify the action of the -M option to fit the documentation

src/ecotag.py

@@ -370,7 +370,7 @@ if __name__=='__main__':
 
         if best[0]:
             taxlist = set(taxonlink[p[0].id] for p in match)
-            if options.error > 0.0 and len(match) >= options.minmatches:
+            if options.error > 0.0 and len(match) >= int(options.minmatches * options.error):
                 lca = taxonomy.betterCommonTaxon(options.error,
                                                  *tuple(taxlist))
             else: