Makefile cleanup: CXXFLAGS, DEPFILES
Simplify base_txn_btree_handler protocol.
Lower overhead for disabled scoped_rcu_regions.

By using a separate disabled_rcu_region type.

I don't trust GCC to optimize the stack allocation (although
honestly it seems to do a pretty good job).
Merge pull request #1 from kohler/master

Cleanups, scoped_rcu_region