fix segfault in DNS mapping lookup code

the allocatorthread got pointers to RAM which were reallocated
behind the back, and if realloc() couldn't grow in-place, lead
to segfaults in applications that do a lot of DNS-lookups such
as webbrowsers.

closes #66
closes #31

thanks to @ravomavain for tracking down the issue.

src/core.c

@@ -37,7 +37,6 @@
 
 #include "core.h"
 #include "common.h"
-#include "shm.h"
 #include "allocator_thread.h"
 
 extern int tcp_read_time_out;