Use MenuItemCompat to fix cast exception bug.

10-21 21:48:02.561: E/AndroidRuntime(31144): java.lang.ClassCastException: android.widget.ShareActionProvider cannot be cast to android.support.v7.internal.view.menu.MenuItemWrapperICS$ActionProviderWrapper
10-21 21:48:02.561: E/AndroidRuntime(31144): 	at android.support.v7.internal.view.menu.MenuItemWrapperICS.getSupportActionProvider(MenuItemWrapperICS.java:311)
10-21 21:48:02.561: E/AndroidRuntime(31144): 	at android.support.v7.internal.view.menu.MenuItemWrapperICS.checkActionProviderOverrideVisibility(MenuItemWrapperICS.java:325)
10-21 21:48:02.561: E/AndroidRuntime(31144): 	at android.support.v7.internal.view.menu.MenuItemWrapperICS.setActionProvider(MenuItemWrapperICS.java:263)
10-21 21:48:02.561: E/AndroidRuntime(31144): 	at com.funkyandroid.droidcon.uk.iosched.util.SessionsHelper.tryConfigureShareMenuItem(SessionsHelper.java:84)
Merge pull request #68 from chrisanderson79/DroidconUK2013

Use MenuItemCompat to fix cast exception bug.