In JOIN_TAB::update_explain_data(), take into account that
- the table that may have pre-sorted is the first non-const table
- Tables that are eliminated by table elimination are marked
  as const tables, but are not present in the Explain data structures

- "ANALYZE $stmt" should discard select's output, but it should still
  evaluate the output columns (otherwise, subqueries in select list
  are not executed)
- SHOW EXPLAIN's code practice of calling JOIN::save_explain_data()
  after JOIN::exec() is disastrous for ANALYZE, because it resets
  all counters after the first execution. It is stopped
  = "Late" test_if_skip_sort_order() calls explicitly update their part
    of the query plan.
  = Also, I had to rewrite I_S optimization to actually have optimization
    and execution stages.

- Testcase for ANALYZE UNION
- Provide r_rows for union result.

- Support tracking for UNIONs, temporary-table based ORDER BYs,
  and both.

-Add analyze_stmt.test/result

MDEV-406: ANALYZE $stmt
- Ported the old patch to new explain code
- New SQL syntax (ANALYZE $stmt)
- ANALYZE UPDATE/DELETE is now supported (because EXPLAIN UPDATE/DELETE is supported)
- Basic counters are calculated for basic kinds of queries
  (still need to see what happens with join buffer, ORDER BY...LIMIT queries, etc)

cannot use &ulint_var (where ulint == unsigned __int64)
where (ulong *) is expected (in uncompress() and in "%lu")

VS doesn't like #ifdefs inside a macro expansion. move them outside

we don't have closed-source plugins

This patch allows up to 64K pages for tables with DYNAMIC, COMPACT 
and REDUNDANT row types. Tables with COMPRESSED row type allows 
still only <= 16K page size. Note that single row size must be
still <= 16K and max key length is not affected.