Introduce whine_realloc

Move few patters with whine_malloc, if (successful) copy+free, to a new
whine_realloc. It should do the same thing, but with a help from OS it
can avoid unnecessary copy and free if allocation of more data after
current data is possible.

Added few setting remanining space to 0, because realloc does not use
calloc like whine_malloc does. There is no advantage of zeroing what we
will immediately overwrite. Zero only remaining space.

src/dnsmasq.h

@@ -1396,6 +1396,7 @@ void *safe_malloc(size_t size);
 void safe_strncpy(char *dest, const char *src, size_t size);
 void safe_pipe(int *fd, int read_noblock);
 void *whine_malloc(size_t size);
+void *whine_realloc(void *ptr, size_t size);
 int sa_len(union mysockaddr *addr);
 int sockaddr_isequal(const union mysockaddr *s1, const union mysockaddr *s2);
 int hostname_order(const char *a, const char *b);