"Include what you use" for tests

Using strcpy/strlen in global namespace requires `<string.h>`. Include
explicitly instead of assuming another SWIG or library header brings it
in.

Examples/test-suite/director_binary_string.i

@@ -8,6 +8,7 @@
 
 %inline %{
 #include <stdlib.h>
+#include <string.h>
 
 #define BUFFER_SIZE_AA 8
 #define BUFFER_SIZE_BB 5

Examples/test-suite/kwargs_feature.i

@@ -128,6 +128,11 @@ struct ExtendingOptArgs1 {};
 struct ExtendingOptArgs2 {};
 %}
 
+// For strlen/strcpy
+%{
+#include <string.h>
+%}
+
 // Varargs
 %warnfilter(SWIGWARN_LANG_VARARGS_KEYWORD) VarargConstructor::VarargConstructor; // Can't wrap varargs with keyword arguments enabled
 %warnfilter(SWIGWARN_LANG_VARARGS_KEYWORD) VarargConstructor::vararg_method; // Can't wrap varargs with keyword arguments enabled

Examples/test-suite/typemap_various.i

@@ -58,6 +58,10 @@ void CheckRetTypemapUsed() {
    /* hello */ delete[] result;
 }
 
+%{
+#include <string.h>
+%}
+
 %inline {
   class FFoo {
   public: