improve the implementation of Net::Ping on windows by avoiding

improve the implementation of Net::Ping on windows by avoiding
fork(), which is pretty heavy-weight for this kind of
application; use non-blocking sockets instead

has been verified to work on Win2k but will need testing on
other flavors of windows

there is a single known failure on windows in 450_service.t (test 18)
due to what appears to be bugs in the ping_syn()/ack() code

p4raw-id: //depot/perl@19535