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/hacklib.c

@@ -1361,23 +1361,6 @@ nh_snprintf(
 
 RESTORE_WARNING_FORMAT_NONLITERAL
 
-/* cast to int or panic on overflow; use via macro */
-int
-FITSint_(lua_Integer i, const char *file, int line){
-    int ret = (int)i;
-    if (ret != i)
-        panic("Overflow at %s:%d", file, line);
-    return (int)i;
-}
-
-unsigned
-FITSuint_(unsigned long long i, const char *file, int line){
-    unsigned ret = (unsigned)i;
-    if (ret != i)
-        panic("Overflow at %s:%d", file, line);
-    return (unsigned)i;
-}
-
 #ifdef ENHANCED_SYMBOLS
 
 /* Unicode routines */