Implemented IsoExternalFilterCommand.behavior bits 1 and 2

which control revocation due to insufficient size reduction.

libisofs/libisofs.h

@@ -4710,7 +4710,11 @@ struct iso_external_filter_command
 
     /* A bit field which controls behavior variations:
      * bit0= Shortcut: 0 sized input will surely yield 0 sized output
-     * >>> not implemented yet: bit1= Do not install filter if the output becomes larger than the input
+     * bit1= Do not install filter if the output is not smaller than the input
+     * bit2= Do not install filter if the number of output blocks is
+     *       not smaller than the number of input blocks. Block size is 2048.
+     *       Assume that non-empty input yields non-empty output and thus do
+     *       not attempt to attach a filter to files smaller than 2048 bytes.
      */
     int behavior;
 };