This worklog extends ANALYZE TABLE with histogram support. This
allows user to create, update and remove histogram statistics with
the following two syntaxes:

  ANALYZE TABLE tbl_name UPDATE HISTOGRAM ON column [, column] WITH n BUCKETS;
  ANALYZE TABLE tbl_name DROP HISTOGRAM ON column [, column];

mysql.column_stats is converted into a pure dictionary table. This will
allow us to use existing data dictionary machinery to insert, update
and remove histogram data. It will also give us caching mechanism which
we need in future work.

In order to inspect the histogram data, we have added a new view named
information_schema.COLUMN_STATISTICS. Also, mysqlpump and mysqldump is
extended such that ANALYZE TABLE-statements are dumped in order to
re-create histogram statistics.

Change-Id: Ibaff7248698984672d3456063d28af7dcd5a4f82