at error, forget old "success" in .cmdtest-filter

with this changes a test will be re-run again even if
it is restored to an earlier content.
(all this is about the effect of the -i option)

bin/cmdtest.rb

@@ -179,6 +179,7 @@ module Cmdtest
           runner.method_filter.success(method_id)
         rescue Cmdtest::AssertFailed => e
           clog.assert_failure(e.message)
+          runner.method_filter.failure(method_id)
         rescue => e
           io = StringIO.new
           io.puts "CAUGHT EXCEPTION:"
@@ -186,6 +187,7 @@ module Cmdtest
           io.puts "BACKTRACE:"
           io.puts e.backtrace.map {|line| "  " + line }
           clog.assert_error(io.string)
+          runner.method_filter.failure(method_id)
         end
       end
     ensure

lib/cmdtest/methodfilter.rb

@@ -63,6 +63,10 @@ module Cmdtest
       @new_filter[method_id.key] = _get_method_signature(method_id)
     end
 
+    def failure(method_id)
+      @new_filter.delete(method_id.key)
+    end
+
     def _maybe_read_ruby_file(file)
       return if @files_read[file]
       @files_read[file] = true