Generate wrapper aliases only if requested and not by default

Defining the aliases by default results in conflicts when including
headers from multiple modules as e.g. SWIG_PendingException_get() is
defined in all of them, and could also easily result in other unwanted
clashes, so make this opt-in and update the examples and tests relying
on using the wrappers without the module prefix to define
SWIG_DEFINE_WRAPPER_ALIASES explicitly.

Examples/c/exception/runme.c

@@ -5,6 +5,7 @@
 #include <stdio.h>
 #include <assert.h>
 
+#define SWIG_DEFINE_WRAPPER_ALIASES
 #include "example_wrap.h"
 
 static void show_exception(const char* prefix) {