Moved two helper-lemmas to HelperProofs, and shortened two older proofs by use them.
Merge branch 'master' of github.com:nicolaidahl/BPlusTrees
Merge branch 'master' of github.com:nicolaidahl/BPlusTrees

Conflicts:
	code/AppearsInTree.v
	code/InsertProofs.v
	code/Makefile
Proved find_subtree_impl_key_appears.