GNUmakefile: let inclusion of .c files verbatim
.gitignore: .t.c files were incorrectly ignored!
net-client.o: added bare to GNUmakefile and made it compile
net-client.t.c: added test for type declaration of net_client_t
net-client.t.c: assert "new" and "delete" of object
net-client.t.c: add net_client_set_target()
net-client.t.c: added net_client_set_port()
net_client_set_target(): let it work for an IP address