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/CParse/parser.y

@@ -32,7 +32,7 @@
 
 /* We do this for portability */
 #undef alloca
-#define alloca malloc
+#define alloca Malloc
 
 /* -----------------------------------------------------------------------------
  *                               Externals

Source/CParse/templ.c

@@ -620,7 +620,7 @@ static Node *template_locate(String *name, Parm *tparms, Symtab *tscope) {
 	int parms_len = ParmList_len(parms);
 	int *priorities_row;
 	max_possible_partials = Len(partials);
-	priorities_matrix = (int *)malloc(sizeof(int) * max_possible_partials * parms_len); /* slightly wasteful allocation for max possible matches */
+	priorities_matrix = (int *)Malloc(sizeof(int) * max_possible_partials * parms_len); /* slightly wasteful allocation for max possible matches */
 	priorities_row = priorities_matrix;
 	for (pi = First(partials); pi.item; pi = Next(pi)) {
 	  Parm *p = parms;
@@ -818,7 +818,7 @@ success:
     Printf(stdout, "    chosen template:'%s'\n", Getattr(n, "name"));
   }
   Delete(parms);
-  free(priorities_matrix);
+  Free(priorities_matrix);
   return n;
 }