'Gets the set of changed bytes between self and other.'

def changed_bytes(self, other):

    changes = set()
    l.warning('FastMemory.changed_bytes():    This    implementation    is    very    slow    and    only    for    debug    purposes.')
    for (addr, v) in self._contents.iteritems():
        for i in range(self.width):
            other_byte = other.load((addr + i), 1)
            our_byte = v.get_byte(i)
            if (other_byte is our_byte):
                changes.add((addr + i))
    return changes
