Enable building of example/Makefile on Win32

Adding example/.gitignore to ignore *.exe
Appending -lws2_32 at the end of CFLAGS_EXTRA if running make on
Windows to enable easy compiling under that platform.
Obsoletes pull request #454

examples/.gitignore

+*.exe

examples/Makefile

@@ -3,13 +3,18 @@
 
 SUBDIRS = $(sort $(filter-out csharp/, $(dir $(wildcard */))))
 X = $(SUBDIRS)
+ifdef WINDIR
+    # appending the Winsock2 library at the end of the compiler
+	# invocation
+    CFLAGS_EXTRA += -lws2_32
+endif
 
 .PHONY: $(SUBDIRS)
 
 all: $(SUBDIRS)
 
 $(SUBDIRS):
-	@$(MAKE) -C $@
+	@$(MAKE) CFLAGS_EXTRA="$(CFLAGS_EXTRA)" -C $@
 
 clean:
 	for d in $(SUBDIRS) ; do $(MAKE) -C $$d clean ; done