Fail cleanly on allocation failures

Previously code in the SWIG tool didn't handle allocation failures
well.  Most places didn't check for NULL return from
malloc()/realloc()/calloc() at all, typically resulting in undefined
behaviour, and some places used assert() to check for a NULL return
(which is a misuse of assert() and such checks disappear if built with
NDEBUG defined leaving us back with undefined behaviour).

All C allocations are now done via wrapper functions (Malloc(),
Realloc() and Calloc()) which emit and error and exit with non-zero
status on failure, so a non-NULL return can be relied upon.

Fixes #1901.

Source/Swig/wrapfunc.c

@@ -27,7 +27,7 @@ static int Max_line_size = 128;
 
 Wrapper *NewWrapper(void) {
   Wrapper *w;
-  w = (Wrapper *) malloc(sizeof(Wrapper));
+  w = (Wrapper *) Malloc(sizeof(Wrapper));
   w->localh = NewHash();
   w->locals = NewStringEmpty();
   w->code = NewStringEmpty();
@@ -46,7 +46,7 @@ void DelWrapper(Wrapper *w) {
   Delete(w->locals);
   Delete(w->code);
   Delete(w->def);
-  free(w);
+  Free(w);
 }
 
 /* -----------------------------------------------------------------------------