修改PageControl的小圓點大小
http://stackoverflow.com/questions/3409319/is-there-a-way-to-change-page-indicator-dots-color
方法一：重寫setCurrentPage方法即可:

• (void) setCurrentPage:(NSInteger)page {
  [super setCurrentPage:page];
  for (NSUInteger subviewIndex = 0; subviewIndex < [self.subviews count]; subviewIndex++) {
  UIImageView* subview = [self.subviews objectAtIndex:subviewIndex];
  CGSize size;
  size.height = 12;
  size.width = 12;
  [subview setFrame:CGRectMake(subview.frame.origin.x, subview.frame.origin.y,
  size.width,size.height)];
  if (subviewIndex == page) [subview setImage:[UIImage imageNamed:@"BluePoint.png"]];
  else [subview setImage:[UIImage imageNamed:@"BlackPoint.png"]];
  }
  }