Add option to always cache branch pages. Passing existing tests.
Merge branch 'develop' into feature/cache-branches-option
New flag: no_cache_branches. On btree_base::open, set m_cache_branches false if flags::no_cache_branches present. Add "none" flag. Add "-no_cache_branches" option to bt_time.
Increase the statistics available both from the buffer manager and the header. In the header, the number of active leaf and branch nodes is added, as this is helpful in understanding timing and caching issues. bt_time now outputs the buffer and header information and stats. Still not sure branch caching is working correctly.
Reformat btree operator<< so that it aligns with buffer_manager operator<< output. Rework both to be more informative. Add reporting using these to bt_time. Add flush() to bt_time so that timing includes any pending activity.