Non-performant fix for non-updating PagerAdapeter

See http://stackoverflow.com/a/7287121/373321 for the reason behind this fix - and for a more optimised idea too.

Haven't implemented more optimised route yet - worried about XamDroid GREF issues if I do
Merge pull request #6 from slodge/patch-1

Non-performant fix for non-updating PagerAdapeter