Fix item clicks on wrapped adapter (Fixes #4)

When a header/footer is added to a ListView, the adapter is
wrapped in a HeaderViewListAdapter. This commit checks for that in the onItemClick method
and handles it appropriately
Fix the itemclick interface. Fixes #5

The OnItemClickListener now mirrors the one from adapter view.
Merge branch 'master' of github.com:JimiSmith/PinnedHeaderListView
Merge branch 'master' of github.com:duncandee/PinnedHeaderListView