"Include what you use" for tests

Many of these tests implicitly required the target language library files to include the headers upstream.

Examples/test-suite/memberin_extend.i

@@ -11,6 +11,7 @@ struct ExtendMe {
 
 %{
 #include <map>
+#include <string.h>
 std::map<ExtendMe*, char *> ExtendMeStringMap;
 void ExtendMe_thing_set(ExtendMe *self, const char *val) {
   char *old_val = ExtendMeStringMap[self];