Make a brk/sbrk emulation.

Mac OS X seems to have some difficulties with brk/sbrk (maybe with the
4MB heap limit), and replace all the allocation logic will be prone to
errors, I'll add a new define and lib to emulate brk/sbrk using more
standard allocation methods. By default the heap is 64MB, it should be
enough.

h/missing_proto.h

@@ -10,4 +10,20 @@ int   brk(void * addr);
 char *mktemp(char *template);
 #endif
 
+#ifdef EMULATE_BRK
+void *sbrk_emu(int increment);
+int   brk_emu(void * addr);
+
+#ifdef sbrk
+#undef sbrk
+#endif
+#ifdef brk
+#undef brk
+#endif
+
+#define sbrk sbrk_emu
+#define brk brk_emu
+
+#endif
+
 #endif /* H_MISSING_H */