Fix achcat buffers and signal handling
Fix achcat buffers and signal handling

* malloc buffer for received messages and resize on ACH_OVERFLOW
* Install signal handler to set shutdown flag and call ach_cancel()

chen0510566/ach,chen0510566/ach,chen0510566/ach,golems/ach,chen0510566/ach,golems/ach,golems/ach,chen0510566/ach,golems/ach,golems/ach,chen0510566/ach,golems/ach