1) Change algs/sitevm.cpp to exclusively use open_and_update and
commit_and_update. commit_and_update is always efficient than commit, and
than update, because a critical section of removing an entry from the
running_versions set is removed when performing update immediately after
commit.

2) Fix CMakeLists of vacation benchmark to remove nonexistant file
(this was needed to get it to build on my machine)