how treat single memref w/ multiple separate unaddr regions?

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on September 07, 2011 11:36:35_

two separate unaddr sequences in same memref: currently 2nd will be
considered a duplicate error since same callstack.

test:
p = malloc(1);
i = _((int_)(p - 2));

valgrind reports just one error (ignores 2nd part):
==14217== Invalid read of size 4
==14217== at 0x8048645: main (free.c:37)
==14217== Address 0x7267026 is 2 bytes before a block of size 1 alloc'd
==14217== at 0x47EDF20: malloc (vg_replace_malloc.c:236)
==14217== by 0x8048639: main (free.c:36)
==14217==

but with a large buffer passed to a syscall it might be useful to get
separate reports rather than ignore or dup

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=581_