Added invalidateLayout implementation for PSTCollectionViewLayout.m
Merge pull request #176 from r618/master

Added invalidateLayout implementation for PSTCollectionViewLayout
Fix to effectively ignoring contentInset with a small contentSize.
Removed the minimum contentSize setter in -[PSTCollectionViewFlowLayout updateItemsLayout].
PSTCVFlowLayout -updateItemsLayout takes into accout PSTGridLayoutSection.sectionMargins to set contentSize.
Merge pull request #177 from loganmoseley/master

-[PSTCollectionViewFlowLayout updateItemsLayout] changes to correct contentSize.
Merge pull request #170 from lono175/master

Fix "targetContentOffsetForProposedContentOffset:withScrollingVelocity:" not called
Preserve ivar layout.
Fixed createPreparedCellForItemAtIndexPath:layoutAttributes: not applying attributes
Fixed nil return from layoutAttributesForElementsInRect resulting in all cells being removed.
Merge pull request #179 from tyrone-sudeium/bugfix/nil-layout-attributes

Behaviour when layoutAttributesForElementsInRect is nil
Merge pull request #178 from tyrone-sudeium/bugfix/attributes-not-applied

CreatePreparedCellForItem... doesn't apply attributes.
Fixed cell highlighting inconsistences with iOS6, including the order and number of calls
Modified SelectionDelegateExample for better highlighting/selection debugging (in the future)
Add shouldDeselectItemAtIndexPath delegate check; update SelectionDelegateExample accordingly
Merge branch 'master' into fix_highlight
Fix highlighting behavior when touches move; cells should unhighlight immediately when scrolling happens
Fixed crash where the array oldToNewIndexMap was accessed with oldGlobalIndex, a huge number that is out of range.
Merge pull request #181 from taiyangc/fix_highlight

Fix highlight
Merge pull request #180 from neoneye/master

Fixed crash in [PSTCollectionView updateWithItems:] oldToNewIndexMap
Exclueded UIButtons from highlighting