when has headerView, some cell can`not selected

[i255979]

i add a header for PSCollectionView, and cause a bug, the index 2 (sometimes other) cell have no selected event dispatch. i debug it, and found that it cause by the NSStringFromCGRect and CGRectFromString, the two method "not completely interchangeable" i fix the bug by create a new method instead of NSStringFromCGRect. and all is ok.

+(NSString *)toString:(CGRect)frame{ return [NSString stringWithFormat:@"{{%f, %f}, {%f, %f}}", frame.origin.x, frame.origin.y, frame.size.width, frame.size.height]; }