Fixed signal handling
- non-portable signal code moved to zsys
- zsys_handlers_set (NULL) to prevent CZMQ installing its handlers
- note: no longer a side-effect of setting zctx_interrupted to 1
- zsys_handlers_reset () at exit to restore default handlers
It would be cool to get this working on Windows too but I don't have a Windows box.
Xitami seems to be doing it by using a 5x shorter select() timeout (200ms) when under Windows.