implement realloc() for MONITOR_HEAP or vice versa

Add new routine 're_alloc()' that functions as MONITOR_HEAP-aware
libc realloc().  'nhrealloc()' is the version that passes source
file and line info if built with MONITOR_HEAP enabled.  The heaplog
data might now contain '<' (freed by realloc), '>' (replacement
allocation by realloc), and '*' (resized by realloc) entries in
addition to the previous '+' (allocated) and '-' (freed) entries.
heaputil has already been updated in the NHinternal repository.

Move FITSint_() and FITSuint_() from hacklib.c to alloc.c so that
they can be accessed by miscellaneous utility programs.

Remove three or four copies of FITSint_() that were duplicated in
utility programs like dlb and tile2bmp due to those not having
access to src/hacklib.o.  They do have access to src/alloc.o (and
util/panic.o).

src/nhlua.c

@@ -2255,11 +2255,8 @@ nhl_alloc(void *ud, void *ptr, size_t osize, size_t nsize)
         free(ptr);
         return NULL;
     }
-    /*
-     * FIXME:
-     *  Use of realloc() confuses MONITOR_HEAP.
-     */
-    return realloc(ptr, nsize);
+
+    return re_alloc(ptr, nsize);
 }
 
 static int