PATCH: Bug that might cause multiple free's for the same pointers

Please find attached a very small patch that fixes a problem that causes
free_channel to free streams even if they  were previously deleted through
HTChannel_deleteInput or HTChannel_deleteOutput.

This bug seems to be triggered library-wise by the FTP code only.

Could somebody confirm that this patch is correct in its spirit? I
believe that for the TIMEOUT or INTERRUPTED case the current behaviour is
correct...

peter