fix THP bug introduced when we moved to 3.9 kernel

The THP bug was a two stage bug:

	1. we didn't check the pmd correctly and where missing THP : a bad pmd can be a THP
	2. during the shrink page list operation, when we scan the VMA to find if a page belong to a MR we do not release the VMA lock. However this lock can be grabbed by split_huge_page